Showing papers by "University of Göttingen published in 1991"

Pre-Botzinger Complex: A Brainstem Region That May Generate Respiratory Rhythm in Mammals

Abstract: The location of neurons generating the rhythm of breathing in mammals is unknown. By microsection of the neonatal rat brainstem in vitro, a limited region of the ventral medulla (the pre-Botzinger Complex) that contains neurons essential for rhythmogenesis was identified. Rhythm generation was eliminated by removal of only this region. Medullary slices containing the pre-Botzinger Complex generated respiratory-related oscillations similar to those generated by the whole brainstem in vitro, and neurons with voltage-dependent pacemaker-like properties were identified in this region. Thus, the respiratory rhythm in the mammalian neonatal nervous system may result from a population of conditional bursting pacemaker neurons in the pre-Botzinger Complex.

Gene deletions causing human genetic disease: mechanisms of mutagenesis and the role of the local DNA sequence environment

Abstract: Reports describing short (< 20 bp) gene deletions causing human genetic disease were collated in order to study underlying causative mechanisms. Deletion break-point junction regions were found to be non-random both at the nucleotide and dinucleotide sequence levels, an observation consistent with an endogenous sequencedirected mechanism of mutagenesis. Direct repeats of between 2 bp and 8 bp were found in the immediate vicinity of all but one of the 60 deletions analysed. Direct repeats are a feature of a number of recombination, replication or repair-based models of deletion mutagenesis and the possible contribution of each to the spectrum of mutations examined was assessed. The influence of parameters such as repeat length and lenght of DNA between repeats was studied in relation to the frequency, location and extent of these deletions. Findings were broadly consistent with a slipped mispairing model but the predicted deletion of one whole repeat copy was found only rarely. A modified version of the slipped mispairing hypothesis was therefore proposed and was shown to possess considerable explanatory value for ∼ 25% of deletions examined. Whereas the frequency of inverted repeats in the vicinity of gene deletions was not significantly elevated, these elements may nevertheless promote instability by facilitating the formation of secondary structure intermediates. A significant excess of symmetrical sequence elements was however found at sites of single base deletions. A new model to explain the involvement of symmetric elements in frameshift mutagenesis was devised, which successfully accounted for a majority of the single base deletions examined. In general, the loss of one or a few base pairs of DNA was found to be more compatible with a replication-based model of mutagenesis than with a recombination or repair hypothesis. Seven hitherto unrecognized hotspots for deletion were noted in five genes (AT3, F8, HBA, HBB and HPRT). Considerable sequence homology was found between these different sites, and a consensus sequence (TGA/GA/GG/ TA/C) was drawn up. Sequences fitting this consensus (i) were noted in the immediate vicinity of 41% of the other (sporadic) gene deletions, (ii) were found frequently at sites of spontaneous deletion in the hamster APRT gene, (iii) were found to be associated with many larger human gene deletions/translocations, (iv) act as arrest sites for human polymerase a during DNA replication and (v) have been shown by in vitro studies of human polymerase a to be especially prone to frameshift mutation. It is proposed that dissociation of polymerase a at arrest sites may, by providing a stable single stranded substrate, lead to deletion of a DNA sequence either by slipped mispairing via a number of different secondary structure intermediates, or by strand-switching or base misincorporation. Human gene deletions thus appear to be caused by multiple mechanisms whose relative importance is probably governed by local primary and secondary DNA structure. Our ability to predict precisely the location and extent of a gene deletion is however hampered both by this complexity and by the possibility that these mechanisms may often act in combination.

Phosphorus efficiency of plants. ii, significance of root radius, root hairs and cation-anion balance for phosphorus influx in seven plant species

Abstract: Fohse et al. (1988) have shown that P influx per unit root length in seven plant species growing in a low-P soil varied from 0.6×10-14 to 4.8×10-14 mol cm-1s-1. The objective of this work was to investigate the reasons for these differences. No correlation was found between P influx and root radius, root hairs, cation-anion balance and Ca uptake. However, when root hairs were included in mathematical model calculations, the differences of P influx could be accounted for. These calculations have shown that in soils low in available P, contribution to P uptake by root hairs was up to 90% of total uptake.

Quantification of virus-specific antibodies in cerebrospinal fluid and serum: sensitive and specific detection of antibody synthesis in brain.

Abstract: Specific antibody synthesis in brain could be detected with maximal sensitivity by combining an advanced enzyme immunoassay with a sophisticated evaluation method that involves calculating the ratio between the cerebrospinal fluid (CSF)/serum quotients for specific antibodies (Qspec) and total IgG (QIgG). This Antibody Index (AI = Qspec/QIgG) discriminates between a blood-derived and a pathological, brain-derived specific antibody fraction in CSF and takes into account individual changes in blood/CSF barrier function. For local synthesis of polyclonal IgG in the central nervous system (QIgG greater than QLim), we propose the correction AI = Qspec/QLim (QLim represents that IgG fraction in CSF originating only from blood, calculated from the individual albumin quotient of a single patient). The normal reference range for the AI was between 0.7 and 1.3 (n = 250 control patients for each antibody species). Values of AI greater than or equal to 1.5 indicated a local specific antibody synthesis in the central nervous system. Sensitivity and precision were greatest if we analyzed the virus-specific antibodies in CSF and serum simultaneously with an enzyme immunoassay in continuous concentrations (arbitrary units) instead of titer steps. We have applied the method successfully to antibodies to measles, rubella, herpes simplex, varicella-zoster, human immunodeficiency virus (HIV), and cytomegalovirus, and to anti-Toxoplasma or -Borrelia antibodies. Clinical relevance is demonstrated for an acute zoster virus infection (monospecific response), chronic diseases such as HIV encephalitis with acute opportunistic Toxoplasma infection, and multiple sclerosis (secondary polyspecific response).

Stretch-activated chloride, potassium, and calcium channels coexisting in plasma membranes of guard cells of Vicia faba L.

Abstract: Mechanosensitive ion channels in the plasma membrane of Vicia faba guard cell protoplasts were studied by use of the patch clamp technique. Stretch-activated (SA) channels in outside-out patches were analyzed for channel conductance, kinetics and ion selectivity. We found three distinct SA channels, permeable to Cl−, K+ and Ca2+ and distinguishable from spontaneous (non-SA) channels for these ions on the basis of conductance, kinetics, and voltage-dependence, as well as sensitivity to membrane stretch. In the attached patch configuration, light suction (2 to 10 kPa) reversibly induced channel opening with multiple amplitudes and complex kinetics. The open probability for SA channels increased nonlinearly with pipette suction. In guard cells in situ, these SA channels may mediate ion transport across the plasma membrane directly, as well as influence the activity of non-SA channels via effects on membrane voltage and cytoplasmic calcium. Through such effects, SA channels likely influence volume and turgor regulation of guard cells, and thereby control of leaf gas exchange.

Redox Transfer across the Inner Chloroplast Envelope Membrane

Abstract: In leaves of spinach plants (Spinacia oleracea L.) grown in ambient CO2 the subcellular contents of adenylates, pyridine nucleotides, 3-phosphoglycerate, dihydroxyacetone phosphate, malate, glutamate, 2-oxoglutarate, and aspartate were assayed in the light and in the dark by nonaqueous fractionation technique. From the concentrations of NADP and NADPH determined in the chloroplast fraction of illuminated leaves the stromal NADPH to NADP ratio is calculated to be 0.5. For the cytosol a NADH to NAD ratio of 10−3 is calculated from the assay of the concentrations of NAD, malate, glutamate, aspartate, and 2-oxoglutarate on the assumption that the reactions catalyzed by the cytosolic glutamate oxaloacetate transaminase and malate dehydrogenase are not far away from equilibrium. For the transfer of redox equivalents from the chloroplastic NADPH to the cytosolic NAD two metabolite shuttles are operating across the inner envelope membrane: the triosephosphate-3-phosphoglycerate shuttle and the malate-oxaloacetate shuttle. Although both shuttles would have the capacity to level the redox state of the stromal and cytosolic compartment, this apparently does not occur. To gain an insight into the regulatory processes we calculated the free energy of the enzymic reactions and of the translocation steps involved. From the results it is concluded that the triosephosphate-3-phosphoglycerate shuttle is mainly controlled by the chloroplastic reaction of 3-phosphoglycerate reduction and of the cytosolic reaction of triosephosphate oxidation. The malate-oxaloacetate shuttle is found to be regulated by the chloroplastic NADP-malate dehydrogenase and also by the translocating step across the envelope membrane.

Amino Acid and sucrose content determined in the cytosolic, chloroplastic, and vacuolar compartments and in the Phloem sap of spinach leaves.

Abstract: Amino acid and sucrose contents were analyzed in the chloroplastic, cytosolic, and vacuolar compartments and in the phloem sap of illuminated spinach leaves (Spinacia oleracea L.). The determination of subcellular metabolite distribution was carried out by nonaqueous fractionation of frozen and lyophilized leaf material using a novel three-compartment calculation method. The phloem sap was collected by aphid stylets which had been severed by a laser beam. Subcellular analysis revealed that the amino acids found in leaves are located mainly in the chloroplast stroma and in the cytosol, the sum of their concentrations amounting to 151 and 121 millimolar, respectively, whereas the amino acid concentrations in the vacuole are one order of magnitude lower. The amino acid concentrations in the phloem sap are found to be not very different from the cytosolic concentrations, whereas the sieve tube concentration of sucrose is found to be one order of magnitude higher than in the cytosol. It is concluded that the phloem loading results in a preferential extraction of sucrose from the source cells.

Molecular Basis of Different Forms of Metachromatic Leukodystrophy

Abstract: Background. Metachromatic leukodystrophy is an autosomal recessive inherited lysosomal storage disorder caused by a deficiency of arylsulfatase A. Three forms of the disease can be distinguished according to severity and the age at onset: late infantile (1 to 2 years), juvenile (3 to 16), and adult (>16). Methods and Results. To understand the molecular basis of the different forms of the disease, we analyzed arylsulfatase A alleles associated with metachromatic leukodystrophy. Two alleles (termed I and A) were Identified and accounted for about half of all arylsulfatase A alleles among 68 patients with metachromatic leukodystrophy whom we examined. Sufficient information was available for 66 of the patients to allow classification of their disease. Of the six instances of homozygosity for allele I, all were associated with the late-infantile form of the disease; of the eight instances of homozygosity for allele A, five were associated with the adult form and three with the juvenile form. When bo...

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. II - An intensive study of NGC 5548 at optical wavelengths

Abstract: A large, international program of ground-based optical spectroscopy and photometry of the variable Seyfert 1 galaxy NGC 5548 undertaken in support of an IUE monitoring campaign is described. This contribution presents the data base and describes the methods used to correct for systematic differences between spectra from different sources. Optical continuum and H-beta emission-line light curves are derived from the spectra. The behavior of the optical continuum is qualitatively the same as the behavior of the ultraviolet continuum. Cross-correlation of the ultraviolet and optical continuum measurements does not reveal any significant lag between them. The h-beta emission-line variations show the same basic pattern as seen in the continuum and ultraviolet emission lines, with H-beta lagging behind the continuum by about 20 days. This is significantly larger than the about 10 day lag deduced for Ly-alpha.

Chronic prostatitis: a thorough search for etiologically involved microorganisms in 1,461 patients.

Abstract: The paper summarizes the results of a thorough search for involved microorganisms in 1,461 patients suffering from chronic prostatitis and 202 controls from 1976 to 1988 following a standardized diagnostic program.

Pineal hormone melatonin oscillates also in the dinoflagellate Gonyaulax polyedra

Abstract: Periodic organization represents the basis for temporal orientation corresponding to environmental changes in illumination. The cyclicity in the diurnal light/dark zeitgeber, however, has to be transformed into chemical signals in order to become interpretable by organisms. In our view, it is remarkable that valuable information is not restricted to the presence, but is also provided by the absence of light. With regard to photoperiodism, higher vertebrates, in fact, make preferential use of this latter information and transform the signal \"darkness\" into a high concentration of a chemical mediator, the pineal \"night hormone\", melatonin [ 1 31. The occurrence of melatonin, however, is not restricted to vertebrates. This indoleamine has been shown to exist in insects, too [ 4 7], and to exert effects on reproduction even in planarians [8]. In the dinoflagellate Gonyaulax polyedra, we have recently demonstrated the presence of the enzymes of melatonin formation from serotonin, i.e., indoleamine (\"serotonin\") N-acetyltransferase and hydroxyindole Omethyltransferase [9]. Here, we report on a diurnal rhythm of melatonin concentration in this unicellular organism. Gonyaulax polyedra was grown at 20°C, in a light-dark cycle of 12:12 h (1200:0 Ix; for further details see [11]). Determinations of melatonin by HPLC were based on samples of at least n = 4; maxima were verified on larger samples (1.5 h after lights-off: n = 20; 3 h in darkness: n = 15; 6 and 7.5 h in darkness: n = 12). In the case of RIA, samples amounted in general to n = 5; again, maxima were based on larger numbers (1.5 h in darkness: n = 15; 3 h in darkness: n = 12). Melatonin can be detected in material from Gonyaulax only if special, preservative extraction procedures are applied. Even after denaturation of cell protein, extracts still contain components which can easily destroy melatonin, in particular, after exposure to light [10]. Therefore, the entire procedures were carried out in darkness or dim red light. Melatonin was measured by two independent methods, reversephase HPLC with on-line electrochemical detection, and RIA. Each technique required a particular extraction procedure. In the case of HPLC, cells from 2.7 1 of densely grown Gonyaulax cultures [11] were concentrated to 1 ml by passing them through an 8-/tm mesh membrane filter (Sartorius, GOttingen). This cell suspension was mixed with 1 ml of 1 M Tris-HC1 buffer, pH 8.4, shock-frozen with liquid nitrogen, and pulverized in a mortar; 300 mg of this powder were thoroughly shaken with 300 /zl of 0.4 N PCA containing 0.1 °7o Na2S20 5 and 0.05 °70 EDTA, and extracted for 15 min at 4°C. Precipitates were sedimented for 15 min at 12000 g, and 200 /zl of the supernatant were injected into the HPLC system. Indole compounds including melatonin were separated by isocratic HPLC (Du Pont) on a 10-/zm C18 reverse-phase column, and measured electrochemically (detector: Metrohm) at a potential of 990 mV. The eluent consisted of 2007o methanol, 3.75 g NaH2POJl , 11.25 g citric acid/l, 320 mg octane sulfonic acid/l, and 32 mg EDTA/I (flow rate 0.75 ml/min). Peak identity with melatonin was verified by co-elution with standards under varying elution conditions. The detection limit was 50 pg/200 /,1 injected load. For determination of melatonin by RIA, 1 ml of concentrated Gonyaulax suspension, prepared from 1.35 1 of culture as described, was mixed with 1 ml of 0.1 M tricine NaOH buffer, pH 7.8. After shock-freezing in liquid nitrogen and pulverization in the mortar, 300 mg of powder were extracted with 900 /,1 of acetone for 30 min at 20 °C. A 12000-g supernatant was diluted with an equal volume of water and lyophilized. The lyophilizate was dissolved in 0.1 M tricine NaOH buffer, pH 7.8, containing 9 g NaC1/1, 1 g gelatin/l, and 1 g sodium azide/1, and assayed by RIA [12] using the highly specific antibody batch no. GS 704-6483 from Guildhay Antisera (Guildford, UK). Bound tritium-labeled melatonin was determined by a scintillation proximity assay, on the basis of a double antibody procedure using anti-sheep immunoglobulin bound to scintillator-containing microspheres (Amersham, Braunschweig). Accuracy and specificity of the assay were verified according to criteria of serial dilution, parallelity, and crossreactivity with various tryptophan metabolites. The detection limit of RIA was 10 pg/ml. Protein concentration was determined using a microversion of the method in [13]. In Gonyaulax polyedra, the existence of melatonin can be demonstrated by the two entirely different techniques of reverse-phase HPLC and RIA. Both methods yielded similar data on cellular melatonin content and its diurnal pattern. The amounts of this indoleamine were surprisingly high in the dinoflagellate, reaching values observed in mammalian pineal glands [14, 15]. The concentration of melatonin oscillates within the diurnal cycle, showing a typical pattern (Fig. 1) characterized by a rapid increase after lights-off, followed by a maximum as early as 1.5 h after lights-off, and a subsequent gradual decline already during night, reaching minimal values in the light phase. The diurnal time course of melatonin in Gonyaulax shows remarkable similarities to patterns seen in vertebrates [1 -3 , 14, 15]. The most striking conformity is the strong increase after the onset of darkness. As in

Anticancer Agents, 15. Squaric Acid Diethyl Ester: A New Coupling Reagent for the Formation of Drug Biopolymer Conjugates. Synthesis of Squaric Acid Ester Amides and Diamides

Abstract: Reaction of squaric acid diethyl ester (1) with a slight excess of a primary or secondary amine 2 in ethanol, dichloromethane or aqueous buffer (pH 7) at 20°C for 03–12 h gives the squaric acid amide esters 3 in mostly excellent yields Treatment of 3 with amines 2 or 4 in organic solvents in the presence of triethylamine or in aqueous buffer (pH 9) leads to the corresponding symmetrical and unsymmetrical squaric acid diamides 5, respectively The reaction can be followed by UV spectroscopy

Effects of extracts from Cimicifuga racemosa on gonadotropin release in menopausal women and ovariectomized rats.

Abstract: Remifemin is an ethanolic extract of the rhizome of Cimicifuga racemosa (C.r.) and is used to relieve climacteric hot flushes. In the present study the effects of this preparation on LH and FSH secretion of menopausal women were investigated. After an 8 weeks treatment, LH but not FSH levels were significantly reduced in patients receiving the Cimicifuga extract. To further characterize the endocrinologically active principles of this plant extract, a lipophilic extract of C.r. was prepared and subjected to Sephadex chromatography. Fractions obtained were tested for their ability to reduce LH secretion in ovariectomized (ovx) rats and to compete in vitro with 17 beta-estradiol for estrogen receptor binding sites. Three types of endocrinologically active compounds were obtained: (1) Constituents which were not ligands for the estrogen receptor but suppress LH release after chronic treatment, (2) constituents binding to the estrogen receptor and also suppressing LH release, and (3) compounds which are ligands for the estrogen receptor but without an effect of LH release. It is concluded that the LH suppressive effect of C.r. extracts observed in menopausal women and ovx rats is caused by at least three different synergistically acting compounds.

Inhibitory effect of okadaic acid on the p-nitrophenyl phosphate phosphatase activity of protein phosphatases.

Abstract: The phosphatase activities of type 2A, type 1 and type 2C protein phosphatase preparations were measured against p-nitrophenyl phosphate (pNPP), a commonly used substrate for alkaline phosphatases. Of the three types of phosphatase examined, the type 2A phosphatase exhibited an especially high pNPP phosphatase activity (119 +/- 8 mumol/min per mg of protein; n = 4). This activity was strongly inhibited by pico- to nano-molar concentrations of okadaic acid, a potent inhibitor of type 2A and type 1 protein phosphatases that has been shown to have no effect on alkaline phosphatases. The dose-inhibition relationship was markedly shifted to the right and became steeper by increasing the concentration of the enzyme, as predicted by the kinetic theory for tightly binding inhibitors. The enzyme concentration estimated by titration with okadaic acid agreed well with that calculated from the protein content and the molecular mass for type 2A phosphatase. These results strongly support the idea that the pNPP phosphatase activity is intrinsic to type 2A protein phosphatase and is not due to contamination by alkaline phosphatases. pNPP was also dephosphorylated, but at much lower rates, by type 1 phosphatase (6.4 +/- 8 nmol/min per mg of protein; n = 4) and type 2C phosphatase (1.2 +/- 3 nmol/min per mg of protein; n = 4). The pNPP phosphatase activity of the type 1 phosphatase preparation shows a susceptibility to okadaic acid similar to that of its protein phosphatase activity, whereas it was interestingly very resistant to inhibitor 2, an endogenous inhibitory factor of type 1 protein phosphatase. The pNPP phosphatase activity of type 2C phosphatase preparation was not affected by up to 10 microM-okadaic acid.

1.11 – The Knoevenagel Reaction

Abstract: In 1894 Knoevenagel published a paper in the journal Chemisehe Berichte on the reaction of formaldehyde and diethyl malonate in the presence of diethylamine as catalyst.1 He obtained the bis adduct (1). Two years later he was able to show that the reaction of benzaldehyde and ethyl acetoacetate in the presence of piperidine gives the bis adduct (2) at room temperature and at 0 °C the benzylidene-1,3-di- carbonyl (3; Scheme 1).2

Formation of poly(3-hydroxyalkanoates) by phototrophic and chemolithotrophic bacteria

Abstract: The formation of poly(3-hydroxyalkanoic acid), PHA, by various strains of chemolithotrophic and phototrophic bacteria has been examined. Chemolithotrophic bacteria were grown aerobically under nitrogen-limiting conditions on various aliphatic organic acids. Phototrophic bacteria were grown anaerobically in the light on a nitrogen-rich medium and were subsequently transferred to a nitrogen-free medium containing acetate, propionate, valerate, heptanoate or octanoate as carbon source. All 41 strains investigated in this study were able to synthesize and accumulate PHA. All 11 strains of chemolithotrophic bacteria and all 15 strains belonging to the non-sulfur purple bacteria synthesized a polymer, which contained 3-hydroxy-valerate (3HV) beside 3-hydroxybutyrate (3HB), if the cells were cultivated in the presence of propionate, valerate or heptanoate. Many non-sulfur purple bacteria synthesized copolyesters of 3HB and 3HV even with acetate as carbon source. In contrast, most sulfur purple bacteria did not incorporate 3HV at all. Among 15 strains tested, only Chromatium vinosum strain 1611, C. purpuratum strain BN5500 and Lamprocystis roseopersicina strain 3112 were able to synthesize polyesters containing 3HV with propionate, valerate or heptanoate as carbon source.

Chemical composition and fractionation of the continental crust

Abstract: A new estimate of the bulk continental crust is reported consisting of 57 percent lower crust (60% felsic and 40% mafic granulites) and 43 percent upper crust. The proportions of crustal units are based on petrological observations (Bohlen &Mezger, 1989). The estimate of a bulk composition is intermediate between andesite and tonalite and is higher in Si, K, Rb, Sr, Zr, Nb, Ba, LREE, Pb, Th concentrations and lower in Mg, Ca, Sc, Mn, Fe than the crustal abundances reported byTaylor &McLennan (1985). Equal chemical composition between the upper crust and the felsic part of the lower crust is attained in balance computations if one restores a fraction of 12.5 percent S-type granite from the upper into the lower crust. An example of water-undersaturated partial melting and separation of a fraction of about 35 percent granitic magma at the conversion from amphibolite-into granulite-facies metasediments has been balanced bySchnetger (1988) in the Ivrea area (N. Italy). The worldwide observed discrepancy between a larger negative Eu anomaly in the upper crust compared with the half as large positive anomaly of the lower crust increasing from the early Precambrian to present has been explained by recycling of Ca-rich restite into the upper mantle. The composition of the Archean crust (example: Greenland) does not differ systematically from the post-Archean crust.

Photoperiodism and effects of indoleamines in a unicellular alga, Gonyaulax polyedra

Abstract: Mediation of photoperiodic effects by indoleamines, especially melatonin, is known in higher vertebrates. A similar mechanism may occur in a unicellular alga, the dinoflagellate Gonyaulax polyedra. This organism entered the dormant stage of a cyst upon short-day treatment at lowered temperatures. Interruption of darkness by 2 hours of light prevented cyst formation, even when the overall duration of light was the same as in cyst-inducing short days. When given in a noninducing photoperiod, melatonin and an analog, 5-methoxytryptamine, substances that had previously been shown to occur in Gonyaulax, provoked cyst formation. Methoxylated indoleamines may play a role as mediators of darkness in this unicellular, in a similar way as in vertebrates, suggesting a common biochemical basis of photoperiodism.

Response of the medullary respiratory network of the cat to hypoxia.

Abstract: 1. The effect of systemic hypoxia was tested in anaesthetized, immobilized, thoracotomized and artificially ventilated cats with peripheral chemoreceptor afferents either intact or cut. Extracellular recordings from different types of medullary respiratory neurones and intracellular recordings from stage 2 expiratory neurones were made to determine the hypoxia-induced changes in neuronal discharge patterns and postsynaptic activity as an index for the disturbances of synaptic interaction within the network. 2. The general effect of systemic hypoxia was an initial augmentation of respiratory activity followed by a secondary depression. In chemoreceptor-denervated animals, secondary depression led to central apnoea. 3. The effects of systemic hypoxia were comparable with those of cerebral ischaemia following occlusion of carotid and vertebral arteries. 4. In chemoreceptor-denervated animals, all types of medullary respiratory neurones ceased spontaneous action potential discharge during hypoxia. 5. Reversal of inhibitory postsynaptic potentials (IPSPs) and/or blockade of IPSPs was seen after 2-3 min of hypoxia. 6. During hypoxia, the membrane potential of stage 2 expiratory neurones showed a slight depolarization to -45 to -55 mV and then remained stable. 7. The neurone input resistance increased initially and then decreased significantly during central apnoea. 8. Rhythmogenesis of respiration was greatly disturbed. This was due to blockade of IPSPs and, in some animals, to more complex disturbances of phase switching from inspiration to expiration. 9. Central apnoea occurred while respiratory neurones were still excitable as shown by stimulus-evoked orthodromic and antidromic action potentials. 10. The results indicate that the medullary respiratory network is directly affected by energy depletion. There is indication for a neurohumoral mechanism which blocks synaptic interaction between respiratory neurones in chemoreceptor-intact animals.

Purification and properties of a hyperthermoactive α-amylase from the archaeobacterium Pyrococcus woesei

Abstract: The cultivation of the hyperthermophilic archaeobacterium Pyrococcus woesei on starch under continuous gassing (80% H2:20% CO2) caused the formation of 250 U/l of an extremely thermoactive and thermostable α-amylase. In a complex medium without elemental sulphur under 80% N2 and 20% CO2 atmosphere enzyme production could be elevated up to 1000 U/l. Pyrococcus woesei grew preferentially on poly-and oligosaccharides. The amylolytic enzyme formation was constitutive. Enzyme production was also observed in continuous culture at dilution rates from 0.1 to 0.4 h-1. A 20-fold enrichment of α-amylase was achieved after adsorption of the enzyme onto starch and its desorption by preparative gel electrophoresis. The α-amylase consisted of a single subunit with a molecular mass of 70 000 and was catalytically active at a temperature range between 40°C and 130°C. Enzymatic activity was detected even after autoclaving at a pressure of 2 bars at 120°C for 5 h. The purified enzyme hydrolyzed exclusively α-1,4-glycosidic linkages present in glucose polymers of various sizes. Unlike many α-amylases from anaerobes the enzyme from P. woesei was unable to attack short chain oligosaccharides with a chain length between 2 and 6 glucose units.

Plant growth hormones control voltage-dependent activity of anion channels in plasma membrane of guard cells

Abstract: THE opening of stomatal pores in the epidermis of plant leaves is caused by an increase in turgor pressure of the guard cells as a result of the accumulation of potassium salts1,2. Although growth hormones have been shown to affect stomatal opening3, the transduction pathways by which growth regulators exert their effects on stomatal action are largely unknown. Here we report that auxins can elicit stomatal opening. These phytohormones modulate anion channels4,5 in the plasma membrane in what may be an initial step in regulated volume increase in guard cells. Our patch-clamp experiments demonstrate that auxins can directly interact with the extracellular face of the channel. As a result, its activation potential is shifted towards the resting potential of the cell to favour transient channel opening.

Plenary paper 2: Why is the agriculture of advanced Western economies still organized by family farms? Will this continue to be so in the future?

Abstract: The dominance and persistency of family farms in industrialized nonsocialist countries can only be explained by the theory that farm households organize agricultural and household production, and also very often off-farm employment, efficiently. The organizational unity of farms and households in agriculture has to be seen as a consequence of limited economies of size relative to the size of the family's labor capacity. Economies of size are increasing as well as labor capacity due to labor saving technological innovations. Smaller than technically "optimal" farm sizes are further to be explained by lower transaction costs of family farms vis-a-vis hired labor farms. Future changes of these determinants and their implications for family farming are discussed. Copyright 1991 by Oxford University Press.

The Ideal and Reality of the Republic of Letters in the Enlightenment

Abstract: The Republic of Letters of the late seventeenth and eighteenth centuries teaches us two lessons about style in science. First, the bearer of style—individual, nation, institution, religious group, region, class—depends crucially on historical context. When the organization and values of intellectual life are self-consciously cosmopolitan, and when allegiances to other entities (e.g., Protestant versus Catholic, or urban versus rural) are culturally more compelling than those to the nation-state, distinctively national styles are far to seek. This was largely the case for the Republic of Letters, that immaterial (it lacked location, formal administration, and brick and mortar) but nonetheless real (it exercised dominion over thoughts and deeds) realm among the sovereign states of the Enlightenment. Second, that form of objectivity which made science seem so curiously detached from scientists, and therefore so apparently unmarked by style at any level, also has a history. The unremitting emphasis on impartial criticism and evaluation within the Republic of Letters encouraged its citizens to distance themselves first from friends and family, then from compatriots and contemporaries, and finally, in the early nineteenth century, from themselves as well. Although this psychological process of estrangement and ultimately of self-estrangement may seldom have been completely realized, the striving was genuine and constitutes part of the moral history of objectivity.

Sequence of the Candida albicans gene encoding the secretory aspartate proteinase.

Abstract: The gene encoding the Candida albicans aspartate proteinase that is secreted by cells grown in protein-containing media was cloned from a C. albicans genomic bank. The base sequence of the insert shows a 1173 bp open-reading frame and indicates an amino acid sequence typical of aspartate proteinases, with amino acid sequence homology to other enzymes of this class and a putative signal peptide consisting of 50 amino acids upstream of the active enzyme.

Natural transfer of conjugative transposon Tn916 between gram-positive and gram-negative bacteria.

Abstract: The conjugative streptococcal transposon Tn916 was found to transfer naturally between a variety of gram-positive and gram-negative eubacteria. Enterococcus faecalis hosting the transposon could serve as a donor for Alcaligenes eutrophus, Citrobacter freundii, and Escherichia coli at frequencies of 10(-6) to 10(-8). No transfer was observed with several phototrophic species. Mating of an E. coli strain carrying Tn916 yielded transconjugants with Bacillus subtilis, Clostridium acetobutylicum, Enterococcus faecalis, and Streptococcus lactis subsp. diacetylactis at frequencies of 10(-4) to 10(-6). Acetobacterium woodii was the only gram-positive organism tested that did not accept the transposon from a gram-negative donor. The results prove the ability of conjugative transposable elements such as Tn916 for natural cross-species gene transfer, thus potentially contributing to bacterial evolution.

An ecosystem approach to soil acidification.

Abstract: With respect to soil acidification, two aspects must be considered: 1. Soil acidification is the consequence of the formation or input of acids. Carbonate and silicate rocks are weak bases. Therefore soils cannot acidify as the consequence of rock weathering (exception: sulfide rocks, the content of sulfides in silicate rocks is usually negligible). Rainwater of pH > 5 possesses alkalinity and cannot therefore acidify soils. The main acid source remaining are the organisms due to their life processes. This chapter deals mainly with an approach to quantify the rate of formation of acidity due to the life processes in the ecosystem. Since man has changed the acid/base status of aerosols, cloud water and all types of precipitation from alkalinity to acidity, the rate of acid deposition has to be considered as well. 2. With respect to the life processes of the organisms existing in an ecosystem, the soil represents the reaction vessel. The second aspect of soil acidification is represented by the chemical reactions taking place in this reaction vessel. This aspect is not treated in detail in this chapter, but elsewhere in this volume.