Showing papers by "University of Göttingen published in 1993"

Preserved incretin activity of glucagon-like peptide 1 [7-36 amide] but not of synthetic human gastric inhibitory polypeptide in patients with type-2 diabetes mellitus.

Abstract: In type-2 diabetes, the overall incretin effect is reduced. The present investigation was designed to compare insulinotropic actions of exogenous incretin hormones (gastric inhibitory peptide [GIP] and glucagon-like peptide 1 [GLP-1] [7-36 amide]) in nine type-2 diabetic patients (fasting plasma glucose 7.8 mmol/liter; hemoglobin A1c 6.3 +/- 0.6%) and in nine age- and weight-matched normal subjects. Synthetic human GIP (0.8 and 2.4 pmol/kg.min over 1 h each), GLP-1 [7-36 amide] (0.4 and 1.2 pmol/kg.min over 1 h each), and placebo were administered under hyperglycemic clamp conditions (8.75 mmol/liter) in separate experiments. Plasma GIP and GLP-1 [7-36 amide] concentrations (radioimmunoassay) were comparable to those after oral glucose with the low, and clearly supraphysiological with the high infusion rates. Both GIP and GLP-1 [7-36 amide] dose-dependently augmented insulin secretion (insulin, C-peptide) in both groups (P < 0.05). With GIP, the maximum effect in type-2 diabetic patients was significantly lower (by 54%; P < 0.05) than in normal subjects. With GLP-1 [7-36 amide] type-2 diabetic patients reached 71% of the increments in C-peptide of normal subjects (difference not significant). Glucagon was lowered during hyperglycemic clamps in normal subjects, but not in type-2 diabetic patients, and further by GLP-1 [7-36 amide] in both groups (P < 0.05), but not by GIP. In conclusion, in mild type-2 diabetes, GLP-1 [7-36 amide], in contrast to GIP, retains much of its insulinotropic activity. It also lowers glucagon concentrations.

Sequential Transformations in Organic Chemistry: A Synthetic Strategy with a Future†

Abstract: Organic-chemical synthesis has always fascinated chemists and will not lose its importance in the future. It is a truism that all chemists—and others too—are dependent on the synthesis of those compounds with which they want to work. As a result, organic-chemical synthesis today is more than ever before the cutting edge of organic chemistry, biology, biochemistry, medicine, physics, and material science. Synthesis is also the basis of the chemical industry. For the passionate synthetic chemist, however, synthesis is much more than just a method for obtaining compounds; it is the expression of his creativity, intelligence, ability, and also his perseverance.

Normalization of fasting hyperglycaemia by exogenous glucagon-like peptide 1 (7-36 amide) in type 2 (non-insulin-dependent) diabetic patients.

Abstract: Glucagon-like peptide 1 (GLP-1) (7-36 amide) is a physiological incretin hormone that is released after nutrient intake from the lower gut and stimulates insulin secretion at elevated plasma glucose concentrations. Previous work has shown that even in Type 2 (non-insulin-dependent) diabetic patients GLP-1 (7-36 amide) retains much of its insulinotropic action. However, it is not known whether the magnitude of this response is sufficient to normalize plasma glucose in Type 2 diabetic patients with poor metabolic control. Therefore, in 10 Type 2 diabetic patients with unsatisfactory metabolic control (HbA1c 11.6 +/- 1.7%) on diet and sulphonylurea therapy (in some patients supplemented by metformin or acarbose), 1.2 pmol x kg-1 x min-1 GLP-1 (7-36 amide) or placebo was infused intravenously in the fasting state (plasma glucose 13.1 +/- 0.6 mmol/l). In all patients, insulin (by 17.4 +/- 4.7 nmol x 1-1 x min; p = 0.0157) and C-peptide (by 228.0 +/- 39.1 nmol x 1-1 x min; p = 0.0019) increased significantly over basal levels, glucagon was reduced (by -1418 +/- 308 pmol x 1-1 x min) and plasma glucose reached normal fasting concentrations (4.9 +/- 0.3 mmol/l) within 4 h of GLP-1 (7-36 amide) administration, but not with placebo. When normal fasting plasma glucose concentrations were reached insulin returned towards basal levels and plasma glucose concentrations remained stable despite the ongoing infusion of GLP-1 (7-36 amide). Therefore, exogenous GLP-1 (7-36 amide) is an effective means of normalizing fasting plasma glucose concentrations in poorly-controlled Type 2 diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Additive insulinotropic effects of exogenous synthetic human gastric inhibitory polypeptide and glucagon-like peptide-1-(7-36) amide infused at near-physiological insulinotropic hormone and glucose concentrations.

Abstract: Gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1-(7-36) amide (GLP-1) are glucose-dependent insulinotropic gut hormones that may explain the greater insulin secretory response with oral compared to i.v. glucose (incretin effect). To study their individual and combined contributions, in eight healthy volunteers, on separate occasions, synthetic human GIP (1 pmol/kg.min) and/or GLP-1 (0.3 pmol/kg.min) or placebo were infused i.v. (-30 to 120 min), while at 0 min, a glucose infusion "isoglycemic" to the profile after an oral glucose load of 50 g/400 mL was started. After the administration of 50 g oral glucose, immunoreactive GIP rose several-fold to 337 +/- 43 pmol/L, while there was only a transient (10-30 min) and moderate increment in immunoreactive GLP-1 (from basal, 25-30, to 41 +/- 4 pmol/L). Isoglycemic i.v. glucose infusions led to smaller B-cell responses (estimated incretin effect, 41 +/- 5%). With single infusions of GIP or GLP-1 (circulating concentrations, 464 +/- 73 and 54 +/- 3 pmol/L, respectively), B-cell responses were significantly augmented compared to i.v. glucose alone and were no longer significantly different from those after oral glucose. The combination of GIP and GLP-1 led to B-cell responses that were significantly higher than those with either hormone alone (additive mode of cooperation). Plasma GIP concentrations were similar after endogenous secretion (oral glucose) and i.v. infusion, while exogenously administered GLP-1 led to plasma levels that were maintained at an elevated level for a longer period during exogenous infusion than after stimulation by oral glucose. When, in seven volunteers, a lower dose (0.15 pmol/kg.min) of GLP-1 was infused during isoglycemic glucose infusion experiments only for the duration of elevated plasma levels in the oral glucose challenges (0-30 min), a significant, but transient, increment in insulin and C-peptide concentrations was observed, which was equivalent to 26 +/- 10% of the estimated incretin effect. Therefore, in conclusion, circulating GIP seems to make a major contribution to the incretin effect after oral glucose, and GLP-1 appears to mediate a smaller proportion. GIP and GLP-1 can interact in an additive manner in normal man.

Sequentielle Transformationen in der Organischen Chemie eine Synthesestrategie mit Zukunft

Abstract: Die organisch-chemische Synthese hat stets eine grose Faszination auf den Chemiker ausgeubt, und sie wird auch in Zukunft nichts von ihrer Bedeutung verlieren. Es ist eine Binsenweisheit, das alle Chemiker - und nicht nur die - auf die Synthese chemischer Verbindungen, mit denen sie arbeiten wollen, angewiesen sind. So ist die organisch-chemische Synthese heute mehr denn je die Schnittstelle von Organischer Chemie, Biologie. Biochemie, Medizin, Physik und Materialwissenschaft. Man sollte auch nicht vergessen, das die Grundlage der chemischen Industrie die Synthese ist. Fur den Synthetiker aus Leidenschaft aber ist die Synthese weit mehr als nur Mittel zu dem Zweck, Verbindungen in die Hand zu bekommen; sie ist Ausdruck seiner Kreativitat. Intelligenz und seines handwerklichen Konnens, aber auch seiner Ausdauer.

Perineuronal nets provide a polyanionic, glia-associated form of microenvironment around certain neurons in many parts of the rat brain.

Abstract: The nature and function of previously described perineuronal nets are still obscure. In the present study their polyanionic components were demonstrated in the rat brain using colloidal iron hydroxide (CIH) staining. In subcortical regions, such as the red nucleus, cerebellar, and vestibular nuclei, most neurons were ensheathed by CIH-binding material. In the cerebral cortex perineuronal nets were seen around numerous nonpyramidal neurons. Biotinylated hyaluronectin revealed that hyaluronan occurs in perineuronal nets. Two plant lectins [Wisteria floribunda agglutinin (WFA) and Vicia villosa agglutinin (VVA)] with affinity for N-acetylgalactosamine visualized perineuronal nets similar to those rich in anionic components. Glutamic acid decarboxylase (GAD)-immunoreactive synaptic boutons were shown to occupy numerous meshes of perineuronal VVA-positive nets. Electron microscopically, VVA binding sites were scattered throughout perisynaptic profiles, but accumulated at membranes and in the extracellular space except not in synaptic clefts. To investigate the spatial relationship between glial cell processes and perineuronal nets, two astrocytic markers (S100-protein and glutamine synthetase) were visualized at the light and electron microscopic level. Two methods to detect microglia by the use of Griffonia simplicifolia agglutinin (GSA I-B4) and the monoclonal antibody, OX-42, were also applied. Labelled structures forming perineuronal nets were observed with both astrocytic, but not with microglial, markers. It is concluded that perineuronal nets are composed of a specialized type of glia-associated extracellular matrix rich in polyanionic groups and N-acetylgalactosamine. The net-like appearance is due to perisynaptic arrangement of the astrocytic processes and these extracellular components. Similar to the ensheathment of nodes of Ranvier, perineuronal nets may provide a special ion buffering capacity required around various, perhaps highly active, types of neurons.

Sex determination of infant and juvenile skeletons: I. Morphognostic features

Abstract: Ancient cemeteries are often characterized by a considerable number of infants and young children. Sex differences in childhood mortality, however, could rarely be studied up to now, mainly because there were only few proven traits for sexual determination of immature skeletons. Based on a historic sample of sixty-one children of known sex and age from Spitalfields, London (37 boys, 24 girls), sexually distinctive traits in the mandible and ilium are presented for morphognostic diagnosis. Besides other features, boys typically show a more prominent chin, an anteriorly wider dental arcade, and a narrower and deeper sciatic notch than girls. Most of the traits presented in this study allow individuals between birth and five years of age to be successfully allocated to either sex in 70-90% of the cases.

The contribution of extrapineal sites of melatonin synthesis to circulating melatonin levels in higher vertebrates

Abstract: While the production of melatonin in higher vertebrates occurs in other organs and tissues besides the pineal, the contribution of extrapineal sites of melatonin synthesis such as the retina, the Harderian glands and the gut to circulating melatonin levels is still a matter of debate. The amount of melatonin found in the gastrointestinal tract is much higher than in any other organ including the pineal and the gut appears to make a significant contribution to circulating melatonin at least under certain conditions. The gut has been identified to be the major source of the elevated plasma concentrations of melatonin seen after tryptophan administration and of the changes of circulating melatonin level induced by the feeding regimen. Whereas the circadian and circannual fluctuations of the concentration of melatonin in the blood seem to be triggered by changes of the photoenvironment and its effect of pineal melatonin formation, basal daytime melatonin levels and the extent of their elevation at nighttime appear to be additionally controlled by nutritional factors, such as the amount and the composition of ingested food and therefore availability of tryptophan as a rate-limiting precursor of melatonin formation by the enterochromaffin cells of the gastrointestinal tract.

The evolution of massive stars including mass loss - Presupernova models and explosion

Abstract: The evolution of massive stars of 35, 40, 60, and 85 solar masses is followed through all stages of nuclear burning to the point of Fe core collapse. Critical nuclear reaction and mass-loss rates are varied. Efficient mass loss during the Wolf-Rayet (WR) stage is likely to lead to final masses as small as 4 solar masses. For a reasonable parameterization of the mass loss, there may be convergence of all WR stars, both single and in binaries, to a narrow band of small final masses. Our representative model, a 4.25 solar-mass WR presupernova derived from a 60 solar mass star, is followed through a simulated explosion, and its explosive nucleosynthesis and light curve are determined. Its properties are similar to those observed in Type Ib supernovae. The effects of the initial mass and mass loss on the presupernova structure of small mass WR models is also explored. Important properties of the presupernova star and its explosion can only be obtained by following the complete evolution starting on the main sequence.

Subcellular volumes and metabolite concentrations in barley leaves

Abstract: Metabolite concentrations in subcellular compartments from mature barley (Hordeum vulgare L. cv. Apex) leaves after 9 h of illumination and 5 h of darkness were determined by nonaqueous fractionation and by the stereological evaluation of cellular and subcellular volumes from light and electron micrographs. Twenty one-day-old primary leaves of barley with a total leaf volume of 902 μL per mg chlorophyll were found to be composed of 27% epidermis, 42% mesophyll cells, 6% veins, 4.5% apoplast and 23% gas space. While in epidermal cells 99% of the volume was occupied by the vacuole, mesophyll cells with an average volume of 31.3 pL consisted of 23 pL (73%) vacuole, 4.6 pL (19%) chloroplasts, 2.06 pL (6,7%) cytosol (including smaller organelles and vesicles), 0.34 pL (1%) mitochondria and 107 fL (0.34%) nucleus. The differences between leaves harvested after 9 h of illumination and after 5 h of darkness were in the size of the stromal compartment and the starch grains therein. Subcellular metabolite concentrations were calculated from the compartmental volumes and metabolite contents of the compartments as determined by nonaqueous fractionation. The amino-acid concentrations in stroma and cytosol were rather similar after 9 h of illumination and 5 h of darkness. In contrast, the vacuolar amino-acid concentrations were about one order of magnitude lower than the stroma and cytosol values, and there was a slight increase in concentration after 5 h of darkness.

Density heterogeneities of hepatitis C virus in human sera due to the binding of beta-lipoproteins and immunoglobulins.

Abstract: Heterogeneities in the density of hepatitis C virus RNA-carrying material (HCV-RNA-CM) found in human sera (1.03-1.20 g/cm3) are attributed to the binding of low-density lipoproteins and/or of IgG. In some sera HCV-RNA-CM seems to be nearly totally bound to beta-lipoproteins and cannot be precipitated by anti-IgG (gamma); in others more than 95% of HCV-RNA-CM is bound to IgG and cannot be precipitated by anti-beta-lipoprotein. Furthermore, there are sera from which HCV-RNA-CM can be completely be precipitated by either anti-beta-lipoprotein or anti-IgG (gamma), pointing to a binding of the two serum proteins to the same HCV-RNA-CM. There are other sera from which HCV-RNA-CM can be partially precipitated by the one or the other antiserum, leaving behind fractions, which are bound to beta-lipoprotein or to IgG. HCV-RNA-CM cannot be precipitated from some sera either by anti-beta-lipoprotein or by anti-IgG (gamma).

Characterization of the inducible nickel and cobalt resistance determinant cnr from pMOL28 of Alcaligenes eutrophus CH34

Abstract: From pMOL28, one of the two heavy metal resistance plasmids of Alcaligenes eutrophus strain CH34, we cloned an EcoRI-PstI fragment into plasmid pVDZ'2. This hybrid plasmid conferred inducible nickel and cobalt resistance (cnr) in two distinct plasmid-free A. eutrophus hosts, strains AE104 and H16. Resistances were not expressed in Escherichia coli. The nucleotide sequence of the 8.5-kb EcoRI-PstI fragment (8,528 bp) revealed seven open reading frames; two of these, cnrB and cnrA, were assigned with respect to size and location to polypeptides expressed in E. coli under the control of the bacteriophage T7 promoter. The genes cnrC (44 kDa), cnrB (40 kDa), and cnrA (115.5 kDa) are probably structural genes; the gene loci cnrH (11.6 kDa), cnrR (tentatively assigned to open reading frame 1 [ORF]; 15.5 kDa), and cnrY (tentatively assigned to ORF0ab; ORF0a, 11.0 kDa; ORF0b, 10.3 kDa) are probably involved in the regulation of expression. ORF0ab and ORF1 exhibit a codon usage that is not typical for A. eutrophus. The 8.5-kb EcoRI-PstI fragment was mapped by Tn5 transposon insertion mutagenesis. Among 72 insertion mutants, the majority were nickel sensitive. The mutations located upstream of cnrC resulted in various phenotypic changes: (i) each mutation in one of the gene loci cnrYRH caused constitutivity, (ii) a mutation in cnrH resulted in different expression of cobalt and nickel resistance in the hosts H16 and AE104, and (iii) mutations in cnrY resulted in two- to fivefold-increased nickel resistance in both hosts. These genes are considered to be involved in the regulation of cnr. Comparison of cnr of pMOL28 with czc of pMOL30, the other large plasmid of CH34, revealed that the structural genes are arranged in the same order and determine proteins of similar molecular weights. The largest protein CnrA shares 46% amino acid similarity with CzcA (the largest protein of the czc operon). The other putative gene products, CnrB and CnrC, share 28 and 30% similarity, respectively, with the corresponding proteins of czc.

On the Function of Mitochondrial Metabolism during Photosynthesis in Spinach (Spinacia oleracea L.) Leaves (Partitioning between Respiration and Export of Redox Equivalents and Precursors for Nitrate Assimilation Products).

Abstract: The functioning of isolated spinach (Spinacia oleracea L.) leaf mitochondria has been studied in the presence of metabolite concentrations similar to those that occur in the cytosol in vivo. From measurements of the concentration dependence of the oxidation of the main substrates, glycine and malate, we have concluded that the state 3 oxidation rate of these substrates in vivo is less than half of the maximal rates due to substrate limitation. Analogously, we conclude that under steady-state conditions of photosynthesis, the oxidation of cytosolic NADH by the mitochondria does not contribute to mitochondrial respiration. Measurements of mitochondrial respiration with glycine and malate as substrates and in the presence of a defined malate:oxaloacetate ratio indicated that about 25% of the NADH formed in vivo during the oxidation of these metabolites inside the mitochondria is oxidized by a malate-oxaloacetate shuttle to serve extramitochondrial processes, e.g. reduction of nitrate in the cytosol or of hydroxypyruvate in the peroxisomes. The analysis of the products of the oxidation of malate indicates that in the steady state of photosynthesis the activity of the tricarboxylic acid cycle is very low. Therefore, we have concluded that the mitochondrial oxidation of malate in illuminated leaves produces mainly citrate, which is converted via cytosolic aconitase and NADP-isocitrate dehydrogenase to yield 2-oxoglutarate as the precursor for the formation of glutamate and glutamine, which are the main products of photosynthetic nitrate assimilation.

Carbon and oxygen isotopic covariations in hydrothermal calcites

Abstract: Isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes: (1) mixing between two different fluids which leads to the precipitation of calcite; (2) mixing between fluid and rock: (a) calcite precipitation due to fluid/rock interaction, (b) secondary alteration of primary calcite by interaction with a subsequent fluid The models are derived from mass balance equations A distinction among the three mixing processes can be made on a δ 13C vs δ 18O diagram, which places important constraints on the genesis of hydrothermal mineralization The variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock, temperature, and dissolved carbon species Owing to significant temperature-dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid, the mixing processes may be distinguished by telltale patterns of isotopic data in δ 13C vs δ 18O space In particular, caution must be exercised in postulating the fluid mixing as the cause for mineral deposition This is demonstrated for hydrothermal Pb-Zn deposits in the western Harz Mountains, Germany A positive correlation between δ 13C and δ 18O values is observed for calcites from the Bad Grund deposit in the Upper Harz Two sample profiles through calcite veins show similar correlations with the lowest δ-values at the center of the veins and the highest δ-values at the vein margins Because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike, it is assumed that a fluid/rock interaction is responsible for the observed correlation and thus for the precipitation of calcite A deep-seated fluid is inferred with a δ 13C value of — 7% and a δ 18O value of +10%, as well as H2CO3 as the dominant dissolved carbon species; precipitation temperatures of the calcites are estimated to be about 280 ∼ 170°C Quite different isotopic distributions are observed for calcites from the St Andreasberg deposit in the Middle Harz An alteration model is suggested based mainly on the isotopic distribution through a calcite vein In addition to a primary fluid which has the same isotopic composition as that in the Bad Grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides, an evolved, HCO 3 - -dominant subsurface fluid with δ 13C about -20 ∼ — 15% and δ 18O ≤ 0% is deduced to alter the primary calcite at low temperatures of 70 ∼40°C

Mitotic stability and meiotic variability of the (CAG)n repeat in the Huntington disease gene

Abstract: The gene causing Huntington's disease, an autosomal dominantly inherited, neurodegenerative disorder, has been identified recently. The corresponding mutation is involving an expansion in the number of (CAG)n repeats in the coding region of the Huntington's disease gene on chromosome 4. In this report, we demonstrate the length variation of the repeat in 513 non-HD chromosomes from normal individuals and HD patients showing 23 alleles with 11 to 33 repeats. Analyzing the inheritance of the (CAG)n stretch we found meiotic instability for HD alleles ([CAG]40 to [CAG]75) with a mutation frequency of approximately 0.7, while in 431 meioses of normal alleles only two expansions were identified. The risk of expansion during spermatogenesis is enhanced compared to oogenesis explaining juvenile onset by transmission from affected fathers. Further, the number of (CAG)n copies in an affected individual in relation to the sex of the transmitting parent was evaluated and no significant differences were found. No mosaicism or differences in the repeat lengths were observed in the DNA from different tissues including brain and lymphocytes of two HD patients indicating mitotic stability of the mutation. Therefore, the determination of the repeat number in the DNA of blood lymphocytes is probably representative of all tissues in a patient.

1,25‐Dihydroxyvitamin D3 Exerts Opposing Effects to IL‐4 on MHC Class‐II Antigen Expression, Accessory Activity, and Phagocytosis of Human Monocytes

Abstract: To investigate the differentiation and activation of monocytes, the combined effects of 1,25-dihydroxyvitamin D3 (D3) and IL-4 on human blood monocytes were examined with respect to expression of MHC class-II antigens, accessory activity, and phagocytic capacity. IL-4 was reported to upregulate the expression of MHC class-II antigens and accessory activity of monocytes. The experiments described here demonstrate that D3 inhibits the expression of all three subtypes of MHC class-II antigens (HLA-DR, -DP and -DQ) as well as the accessory activity of monocytes, both in a dose- and time-dependent manner. However, D3 enhances the immunoglobulin- and complement-dependent phagocytosis by monocytes in a dose- and time-dependent manner. When monocytes are treated with both IL-4 and D3, the effects of D3 are reverted by IL-4, suggesting that IL-4 induces the development of monocytes into accessory cells, whereas D3 stimulates differentiation of monocytes into classical macrophages. These findings provide further evidence for the contention that, depending on defined stimuli, monocytes may develop either into accessory cells or into classical macrophages.

Diffuse white matter disease in three children: an encephalopathy with unique features on magnetic resonance imaging and proton magnetic resonance spectroscopy.

Abstract: Amongst 21 children with unclassified white matter diseases three patients could be characterised by an identical clinical picture, magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (MRS) findings as a probably distinct entity. Following a normal early development they later showed rapidly progressive motor symptoms (ataxia, spasticity) leading to severe handicap within one or two years after onset. Later on bulbar symptoms, optic atrophy and epileptic seizures occurred. The MRI showed a diffuse homogeneous hypodensity of the white matter almost identical to the signal of the ventricles. MRS revealed a near total absence of N-acetylaspartate, choline and creatine and an increase of lactate and glucose. One girl and one boy were siblings, indicating an autosomal recessive trait.

Degradation of poly(3-hydroxybutyrate), PHB, by bacteria and purification of a novel PHB depolymerase fromComamonas sp.

Abstract: Bacteria capable of growing on poly(3-hydroxybutyrate), PHB, as the sole source of carbon and energy were isolated from various soils, lake water, activated sludge, and air. Although all bacteria utilized a wide variety of monomeric substrates for growth, most of the strains were restricted to degrade PHB and copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate, P(3HB-co-3HV). Five strains were also able to decompose a homopolymer of 3-hydroxyvalerate, PHV. Poly(3-hydroxyoctanoate), PHO, was not degraded by any of the isolates. One strain, which was identified asComamonas sp., was selected, and the extracellular depolymerase of this strain was purified from the medium by ammonium sulfate precipitation and by chromatography on DEAE-Sephacel and Butyl-Sepharose 4B. The purified PHB depolymerase was not a glycoprotein. The relative molecular masses of the native enzyme and of the subunits were 45,000 or 44,000, respectively. The purified enzyme hydrolyzed PHB, P(3HB-co-3HV), and—at a very low rate—also PHV. Polyhydroxyalkanoates, PHA, with six or more carbon atoms per monomer or characteristic substrates for lipases were not hydrolyzed. In contrast to the PHB depolymerases ofPseudomonas lemoignei andAlcaligenes faecalis T1, which are sensitive toward phenylmethylsulfonyl fluoride (PMSF) and which hydrolyze PHB mainly to the dimeric and trimeric esters of 3-hydroxybutyrate, the depolymerase ofComamonas sp. was insensitive toward PMSF and hydrolyzed PHB to monomeric 3-hydroxybutyrate indicating a different mechanism of PHB hydrolysis. Furthermore, the pH optimum of the reaction catalyzed by the depolymerase ofComamonas sp. was in the alkaline range at 9.4.

Minimal Replicator Theory I: Parabolic Versus Exponential Growth

Abstract: The paper describes an analytical treatment of artificial self-replicating systems. All artificial self-replicating systems known today are minimal replicators in the sense that their kinetic behavior can be rationalized by a common, minimal reaction model which is outlined in the introduction. In the second section, empirical rate equations are introduced which have proven useful for the evaluation of experimental concentration-time profiles. The third section begins with an discussion of reaction models which have been described earlier to explain the autocatalytic synthesis of self-replicating template molecules. It is followed by an analytical treatment of the minimal reaction model: A + B + C⇌ABC→ C 2;⇌ 2C, where C is a self-complementary template molecule, A and B its precursor molecules, ABC a termolecular complex, and C 2 a template duplex. It is assumed that the irreversible formation of C 2 from ABC is the rate limiting step and that the total template concentration is small as compared to its precursors. The analytical expressions derived allow us to estimate the rate and autocatalytic reaction order for synthetic self-replicating systems from the elementary rate and equilibria constants involved. Three limit growth laws for minimal self-replicating systems—termed as parabolic, weak exponential, and strong exponential—can be distinguished. The following section deals with the influence of temperature. Strong exponential growth is to be expected for low temperatures, whereas weak exponential growth should occur at high temperatures. Parabolic growth is expected for average temperatures. Depending on the activation energy of the irreversible step as well as on the enthalpies of the formation of ABC and C 2, the maximum of the autocatalytic rate occurs either at the temperature of the transition from strong exponential to parabolic growth, or, at the temperature of transition from parabolic to weak exponential growth, or, at an average temperature. The analytical results from the treatment of the above minimal reaction model are then compared to results from more realistic models. In particular, it is shown that the formation of a complex AB from A and B makes it difficult to observe strong exponential growth which otherwise might be found at low temperatures.

A new mechanism of work hardening in the late stages of large strain plastic flow in F.C.C. and diamond cubic crystals

Abstract: A new mechanism of work hardening is proposed to explain the athermal hardening in Stage IV of f.c.c. and diamond cubic crystals. The mechanism is related to a cellular dislocation microstructure in which during Stage III, hardening by dislocation accumulation and recovery by various mechanisms occurs primarily in the cell walls. Hardening of the cells is through the build-up of long range misfit stresses that result when the primary dislocation flux cuts trough the geometrically required dislocation density of the cell walls that is associated with the lattice misorientations between cells. Experiments show that these misorientations increase monotonically with increasing strain. There is no recovery in the cells. At the end of Stage III, hardening in the cell walls saturates, but the hardening due to misfit stresses in the cells continues unabated, giving rise to the rate independent hardening of Stage IV. Eventually this hardening is also terminated in Stage V when the misfit stresses inside cells reach a critical level that triggers rate dependent stress relaxation in the cells by secondary glide processes. The new mechanism makes successful predictions for Stage IV processes, including: hardening rate, plastic resistance levels, the gradual increase in hardening rate with plastic resistance, the residual lattice strains on unloading that can be measured with X-ray peak distortions and broadening, and for the Baushinger effect.

The application of direct methods and Patterson interpretation to high-resolution native protein data.

Abstract: Conventional small-molecule methods of solving the phase problem from native data alone, without the use of heavy-atom derivatives, known fragment geometries or anomalous dispersion, have been tested on 0.9 A resolution data for two small proteins: rubredoxin, from Desulfovibrio vulgaris, and crambin. The presence of three disulfide bridges in crambin and an FeS4 unit in rubredoxin enabled automated Patterson interpretation as well as direct methods to be tried. Although both structures were already well established, the known structures were not used in the phasing attempts, except for identifying successful solutions. Direct methods were not successful for crambin, although the correct phases were stable to phase refinement and gave figures of merit clearly superior to any obtained in the ca 500 000 random starting phase sets that were refined. It appears that the presence of an iron atom in rubredoxin reduces the scale of the search problem by many orders of magnitude, but at the cost of producing `over-consistent' phase sets that overemphasize the iron atom and involve partial loss of enantiomorph information. However, about 1% of direct-methods trials were successful for rubredoxin, giving mean phase errors of about 56° (for all E > 1.2) that could be reduced to about 20° by standard E-Fourier recycling methods. Limiting the resolution of the data degraded the quality of the solutions and suggested that the limiting resolution for routine direct-methods solution of rubredoxin is about 1.2 A. With the 0.9 A data, automated Patterson interpretation convincingly finds the three disulfide bridges in crambin and the FeS4 unit in rubredoxin, and in both cases E-Fourier recycling starting from these `heavier' atoms yields almost the complete structure. Whereas crambin could only be solved in this way at very high resolution, rubredoxin could be solved by Patterson interpretation down to 1.6 A. These results emphasize the benefits of collecting protein data to the highest possible resolution, and indicate that when a few `heavier' atoms are present, it may prove possible in favorable cases to solve the phase problem from a single native data set collected to `atomic resolution'.