Showing papers by "University of Marburg published in 1988"

Coherent oscillations: A mechanism of feature linking in the visual cortex?

Abstract: Primary visual coding can be characterized by the receptive field (RF) properties of single neurons. Subject of this paper is our search for a global,second coding step beyond the RF-concept that links related features in a visual scene. In recent models of visual coding, oscillatory activities have been proposed to constitute such linking signals. We tested the neurophysiological relevance of this hypothesis for the visual system. Single and multiple spikes as well as local field potentials were recorded simultaneously from several locations in the primary visual cortex (A17 and A18) using 7 or 19 individually advanceable fibermicroelectrodes (250 or 330 μm apart).Stimulusevoked (SE)-resonances of 35---85 Hz were found in these three types of signals throughout the visual cortex when the primary coding channels were activated by their specific stimuli. Stimulus position, orientation, movement direction and velocity, ocularity and stationary flicker caused specific SE-resonances.Coherent SE-resonances were found at distant cortical positions when at least one of the primary coding properties was similar. Coherence was found1) within a vertical cortex column,2) between neighbouring hypercolumns, and3) between two different cortical areas. We assume that the coherence of SE-resonances is mediated by recurrent excitatory intra- and inter-areal connections via phase locking between assemblies that represent the linking features of the actual visual scene. Visually related activities are, thus, transiently labelled by a temporal code that signalizes their momentary association.

Release of tumor necrosis factor-alpha from macrophages. Enhancement and suppression are dose-dependently regulated by prostaglandin E2 and cyclic nucleotides.

Abstract: PGE2 has previously been shown to suppress various leukocyte functions. In this study, we examined whether PGE2 would affect release of TNF-alpha from rat resident peritoneal macrophages. Two different, dose-dependent effects were observed: low PGE2 concentrations (0.1 to 10 ng/ml) stimulated, whereas higher concentrations (greater than 10 ng/ml) suppressed TNF-alpha release. PGE2-stimulated TNF-alpha production was dependent on de novo protein synthesis and was associated with an intracellular rise of cGMP. The importance of cGMP as an intracellular messenger for PGE2 was confirmed by the following evidence: (1) low PGE2 concentrations preferentially increased cGMP and not cAMP and (2) cGMP, either exogenously added or endogenously generated by sodium nitroprusside, were efficient stimulators of TNF-alpha production. In contrast, agents increasing intracellular cAMP concentrations such as PGE1, higher PGE2 doses, isoproterenol, and theophylline, all suppressed TNF-alpha synthesis. Only resident, but not casein-elicited or Corynebacterium parvum-activated macrophages, were stimulated by low PGE2 concentrations to increase TNF-alpha production. In tumor cytotoxicity assays, PGE2-activated macrophages were active only against TNF-alpha-sensitive target cells. These findings demonstrate that TNF-alpha synthesis in macrophages is up-regulated by cGMP and down-regulated by cAMP, which indicates that cyclic nucleotides act as intracellular messengers for extracellular signals of macrophage activation.

The molecular biology of influenza virus pathogenicity.

Abstract: Publisher Summary It is an accepted concept that the pathogenicity of a virus is of polygenic nature. Because of their segmented genome, influenza viruses provide a suitable system to prove this concept. The studies employing virus mutants and reassortants have indicated that the pathogenicity depends on the functional integrity of each gene and on a gene constellation optimal for the infection of a given host. As a consequence, virtually every gene product of influenza virus has been reported to contribute to pathogenicity, but evidence is steadily growing that a key role has to be assigned to hemagglutinin. As the initiator of infection, hemagglutinin has a double function: (1) promotion of adsorption of the virus to the cell surface, and (2) penetration of the viral genome through a fusion process among viral and cellular membranes. Adsorption is based on the binding to neuraminic acid-containing receptors, and different virus strains display a distinct preference for specific oligosaccharides. Fusion capacity depends on proteolytic cleavage by host proteases, and variations in amino acid sequence at the cleavage site determine whether hemagglutinin is activated in a given cell. Differences in cleavability and presumably also in receptor specificity are important determinants for host tropism, spread of infection, and pathogenicity. The concept that proteolytic activation is a determinant for pathogenicity was originally derived from studies on avian influenza viruses, but there is now evidence that it may also be relevant for the disease in humans because bacterial proteases have been found to promote the development of influenza pneumonia in mammals.

Onset of Turbulence in a Pipe

Abstract: Calcul de la turbulence dans une conduite a partir de l'equation de Navier-Stokes. L'analyse des simulations numeriques revele que de petites perturbations appelees «meres» induisent des perturbations plus importantes appelees «filles». Les «filles» determinent l'aspect de la turbulence tandis que les «meres» controlent le transfert d'energie de l'ecoulement de base au mouvement turbulent

Organization of the actin filament cytoskeleton in the intestinal brush border: a quantitative and qualitative immunoelectron microscope study.

Abstract: In the present study we have used immunogold labeling of ultrathin sections of the intact chicken and human intestinal epithelium to obtain further insight into the molecular structure of the brush-border cytoskeleton. Actin, villin, and fimbrin were found within the entire microvillus filament bundle, from the tip to the basal end of the rootlets, but were virtually absent from the space between the rootlets. This suggests that the bulk of actin in the brush border is kept in a polymerized and cross-linked state and that horizontally deployed actin filaments are virtually absent. About 70% of the label specific for the 110-kD protein that links the microvillus core bundle to the lipid bilayer was found overlying the microvilli. The remaining label was associated with rootlets and the interrootlet space, where some label was regularly observed in association with vesicles. Since the terminal web did not contain any significant amounts of tubulin and microtubules, the present findings would support a recently proposed hypothesis that the 110-kD protein (which displays properties of an actin-activated, myosin-like ATPase) might also be involved in the transport of vesicles through the terminal web. Label specific for myosin and alpha-actinin was confined to the interrootlet space and was absent from the rootlets. About 10-15% of the myosin label and 70-80% of the alpha-actinin label was observed within the circumferential band of actin filaments at the zonula adherens, where myosin and alpha-actinin displayed a clustered, interrupted pattern that resembles the spacing of these proteins observed in other contractile systems. This circular filament ring did not contain villin, fimbrin, or the 110-kD protein. Finally, actin-specific label was observed in close association with the cytoplasmic aspect of the zonula occludens, suggesting that tight junctions are structurally connected to the microfilament system.

The final step in methane formation. Investigations with highly purified methyl-CoM reductase (component C) from Methanobacterium thermoautotrophicum (strain Marburg).

Abstract: Methyl-coenzyme M reductase (= component C) from Methanobacterium thermoautotrophicum (strain Marburg) was highly purified via anaerobic fast protein liquid chromatography on columns of Mono Q and Superose 6. The enzyme was found to catalyze the reduction of methylcoenzyme M (CH3-S-CoM) with N-7-mercaptoheptanoylthreonine phosphate (H-S-HTP = component B) to CH4. The mixed disulfide of H-S-CoM and H-S-HTP (CoM-S-S-HTP) was the other major product formed. The specific activity was up to 75 nmol min-1 mg protein-1. In the presence of dithiothreitol and of reduced corrinoids or titanium(III) citrate the specific rate of CH3-S-CoM reduction to CH4 with H-S-HTP increased to 0.5-2 mumol min-1 mg protein-1. Under these conditions the CoM-S-S-HTP formed from CH3-S-CoM and H-S-HTP was completely reduced to H-S-CoM and H-S-HTP. Methyl-CoM reductase was specific for H-S-HTP as electron donor. Neither N-6-mercaptohexanoylthreonine phosphate (H-S-HxoTP) nor N-8-mercaptooctanoylthreonine phosphate (H-S-OcoTP) nor any other thiol compound could substitute for H-S-HTP. On the contrary, H-S-HxoTP (apparent Ki = 0.1 microM) and H-S-OcoTP (apparent Ki = 15 microM) were found to be effective inhibitors of methyl-CoM reductase, inhibition being non-competitive with CH3-S-CoM and competitive with H-S-HTP.

Selective processing of threat cues in subjects with panic attacks

Abstract: Previous research has demonstrated that patients with generalised anxiety disorder, phobias, and obsessive-compulsive disorder show an attentional bias towards threat cues related to their respective disorders. Two studies are presented that used a modified Stroop colour naming task to assess attentional bias in subjects with panic attacks. In Study 1, 24 panic disorder patients and 24 normal controls were presented three cards containing threat words related to physical harm, separation, or social embarrassment. Colour naming times were compared between these cards and control cards containing matched non-threat words. Reaction time differences in the two groups were in opposite directions, patients tending to be slower in colour naming threat words, and controls, faster. In Study 2, 18 non-clinical panickers and 18 controls were presented cards containing physical threat words, neutral control words, or colour words, respectively. Panickers showed greater interference than controls in colour na...

The human chromophobe cell renal carcinoma: Its probable relation to intercalated cells of the collecting duct

Abstract: In the present study we have examined ten cases of the chromophobe type renal cell carcinoma. This type of tumor is distinguished from the other carcinomas of the kidney with light cytoplasm (formerly called “hypernephroid”) by (a) a positive Hale’s iron colloid stain of the cytoplasm, (b) the occurrence of numerous invaginated vesicles within the cytoplasm that resemble the invaginated vesicles of intercalated cells of the collecting duct system, and (c) a positive immunoreaction of both the plasma membrane and the cytoplasm with antibodies to the epithelial membrane antigen (EMA) and carbonic anhydrase C (CAC), respectively. Unlike oncocytomas, which also express CAC and EMA, the chromophobe renal cell carcinoma does not express the erythrocyte anion exchanger band 3. These findings strongly indicate that chromophobe renal cell carcinomas as well as oncocytomas of the kidney are histogenetically related to the two populations of intercalated cells of the collecting duct system. Thus, both tumors represent examples of renal tumors which disprove the broadly accepted hypothesis that all epithelial tumors of the kidney are histogenetically related to the proximal tubule.

Photomovement in motile microorganisms—ii

Abstract: In our previous review (Nultsch and Hader, 1979) wc had covered the relevant papers on photomovement which had appeared up to that time. The present review covers the recent work starting from 1979 and only occasionally refers to older literature. Since thBt time a number of other reviews have been published on several aspects of photomovement in microorganisms (Hader, 1980; Feinleib. 1980; Foster and Smyth, 1980; Nultsch, 1980a,b. 1984, 1985a; Nultsch and Hader, 1980; Colombetti and Lenci, 1980; Colombetti et al., 1982b; Kivic and Walne, 1983; Poff and Hong, 1982; Haupt, 1983; Poff, 1983; Melkonian and Robenek, 1984). This survey will cover the light-dependent behavior of whole motile unior multicellular organisms but will exclude phototropic bending of organs of fixed plants (for reviews see, e.g. Dennison, 1979; Lipson et al., 1984) as well as light-triggered intracellular movements such as the orientation of chloroplasts (Britz, 1979; Haupt, 1982; Wagner and Grolig, 1985). Many motile microorganisms orient in their habitat using a number of strategies in response t o several external factors which serve as clues to find an optimal position in their environment. These external factors include chemical (MacNab, 1985; Berg, 1985) and temperature (Mizuno et al., 1984; Poff, 1985) gradients, the earth's magnetic (Ofer et ul., 1984; Frankel, 1984; Esquivel and Barros, 1986; Torres de Araujo ef a/., 1986; Stolz ei al., 1986) and gravitational (Bean, 1984; Briegleb ei nl., 1986; Kessler, 1985, 1986) fields as well as mechanical and electric stimuli. Light certainly plays a major role in orientation not only in photosynthetic organisms, which for energetic reasons depend on the availability of solar radiation, but also in non-photosynthetic organisms which use light as a directional clue to move, e.g. to a suitable area for spore development or to escape detrimental radiation which might destroy the intracellular pigments. Motile microorganisms have developed three basically different strategies with which they respond to light (Diehn et al., 1977): Phototaxis describes the directed movement of an organism with respect to the light direction. Positive phototaxis leads an organism (or a population)

Citric-acid cycle, 50 years on. Modifications and an alternative pathway in anaerobic bacteria.

Abstract: Many anaerobic bacteria can completely oxidize organic matter to CO2 with either sulfur, sulfate, or protons as electron acceptor The sulfur-reducing bacteria and one genus of sulfate reducers use a modified citric-acid cycle with a novel anaplerotic sequence as pathway of terminal respiration All other anaerobes use an alternative pathway, in which carbon monoxide dehydrogenase is a key enzyme and in which acetyl-CoA is cleaved into two C1 units at the oxidation level of CH3OH and CO Thus almost 50 years after the discovery of the citric acid cycle by Hans Krebs in 1937, a second pathway for acetyl-CoA oxidation was found

Ribonucleotide reductase of Brevibacterium ammoniagenes is a manganese enzyme.

Abstract: Ribonucleotide reduction and not DNA replication is the site for the specific manganese requirement of DNA synthesis and cell growth in the coryneform bacterium Brevibacterium ammoniagenes. To characterize the metal effect we have isolated and purified ribonucleoside-diphosphate reductase from overproducing bacteria that were first deprived of and then reactivated by manganese ions. Purification on columns of Sephacryl S400, DEAE-cellulose and hydroxyapatite provided an apparently homogeneous enzyme consisting of two protein subunits. These were characterized by affinity chromatography on 2',5'-ADP-Sepharose as nucleotide-binding protein B1 (Mr = 80,000) and catalytic protein B2 (Mr = 100,000, composed of two Mr = 50,000 polypeptides), which were both necessary for activity. In vitro the purified enzyme does not require added metal ions except for an unspecific, twofold activity increase observed in the presence of Mg2+ and other divalent cations. Enzyme activity is inhibited by hydroxyurea (I50 = 2.5 mM). The electronic spectrum with maxima around 455 nm and 485 nm closely resembles that of manganese(III)-containing pseudocatalase and of oxo-bridged binuclear Mn(III) model complexes. Denaturation of the enzyme in trichloroacetic acid liberated an equimolar amount of Mn(II) which was detected by EPR spectroscopy. It was not possible to remove and reintroduce metal ions without loss of enzyme activity. Manganese-deficient cell cultures were also grown in the presence of 54MnCl2. Ribonucleotide reductase activity and radioactivity cochromatographed in several systems. Non-denaturing polyacrylamide gel electrophoresis showed that protein subunit B2 was specifically 54Mn-labeled. All these properties suggest that the ribonucleotide reductase of B. ammoniagenes is a manganese-containing analog of the non-heme-iron-containing reductases of Escherichia coli and eukaryotes.

Epidermal Growth Factor Receptor Expression in Human Lung Cancer Cell Lines

Abstract: Non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cell lines were studied for epidermal growth factor (EGF) receptor expression. All NSCLC cell lines tested (eight of eight) had specific EGF binding sites, whereas only five of 11 SCLC cell lines bound EGF. NSCLC and SCLC cell lines expressed the same type of high affinity EGF binding sites with a Kd of 0.5 to 4.5 nM; however, NSCLC cells bound significantly more EGF than SCLC cell lines. The amount of binding sites in NSCLC cells ranged between 71 and 1,000 fmol/mg of protein and in SCLC cells, between 26 and 143 fmol/mg of protein. The two SCLC cell lines with EGF binding values within the range of NSCLC belonged to the variant subtype of SCLC. By means of an anti-erbB serum and indirect radioimmunoprecipitation, a strong Mr approximately 170,000 protein band could be detected in the NSCLC cell lines. This protein corresponds to the EGF receptor molecule. Its identity was proven by competition with excess erbB antigen for the antibody during the radioimmunoprecipitation. Furthermore, this Mr 170,000 protein exhibited protein kinase activity as evidenced by in vitro autophosphorylation. The radioactivity incorporated into the Mr 170,000 band in radioimmunoprecipitation and protein kinase assays was 10 to 100 times lower in these SCLC cell lines which were positive in the EGF binding assay compared to the NSCLC cell lines. We conclude that NSCLC in contrast to SCLC expresses high levels of EGF receptors which may be used to facilitate the differential diagnosis in some cases of lung cancer. These data suggest that EGF may play a role in growth and differentiation of NSCLC.

Food-induced histaminosis as an epidemiological problem: plasma histamine elevation and haemodynamic alterations after oral histamine administration and blockade of diamine oxidase (DAO).

Abstract: In a randomized controlled trial, 30 pigs were orally treated with histamine (60 mg). In addition, half of the animals underwent a specific blockade of the enzyme diamine oxidase (DAO), which is the main histamine catabolising enzyme in the intestinal tract. Only these DAO-blocked animals exhibited severe clinical symptoms (e.g. hypotension, flush, vomiting) and, in parallel, showed tremendous elevations of plasma histamine levels of up to 160 ng/ml. 3 out of 15 animals in this group died within the experimental period. In contrast, the control animals neither exhibited plasma histamine levels above 5 ng/ml nor had any clinical reactions. These results contradict the current opinion that oral histamine intake in food is not clinically relevant, especially since many commonly used drugs are DAO-inhibitors and approximately 20% of our population take these drugs. Apart from drugs, some other factors (alcohol, spoilt food etc.) can also function via a blockade of DAO as an additional risk. DAO-blockade is therefore a real epidemiological problem. Evidence is presented here for the new disease concept: Food-Induced Histaminosis.

Effects of SO2 exposure on allergic sensitization in the guinea pig.

Abstract: The effect of sulfur dioxide (SO 2 ) exposure on local bronchial sensitization to inhaled antigen was studied in the guinea pig. Exposure to SO 2 (0.1 to 16.6 ppm) was performed in a 20 L exposure chamber for 8 hours on 5 consecutive days, while temperature, moisture, and concentration of SO 2 were monitored and kept constant. SO 2 concentrations were measured hourly by Schiff's reaction. On the last 3 days, SO 2 exposure was followed by inhalation of nebulized ovalbumin (OA) for 45 minutes. One week later, specific bronchial provocation with inhaled OA (0.1%) followed by plethysmographic measurements of airway obstruction were performed every 2 days during a 2-week period. Specific antibodies against OA were measured in serum and bronchoalveolar fluid by a direct enzyme immunoassay. The SO 2 -exposed group (N = 17) demonstrated 67% to 100% positive bronchial reactions to inhaled OA, depending on the concentration of SO 2 , whereas the control group without previous SO 2 exposure (N = 14) demonstrated bronchial reactions in only one animal (7%: p 2 concentrations ( p 2 -exposed groups significantly, compared to the control group ( p 2 in low and medium concentrations can facilitate local allergic sensitization in the guinea pig.

Adenocarcinomas of the inner nose after exposure to wood dust. Morphological findings and relationships between histopathology and clinical behavior in 79 cases.

Abstract: We present the results of light microscopic, available electron microscopic and immunohistochemical investigations of 79 adenocarcinomas occurring in the noses of wood workers following exposure to beechwood and oakwood dust. Three types of adenocarcinomas can be differentiated. The most frequently occurring form is the papillary tubular cylinder cell adenocarcinoma, while the mucus-producing alveolar goblet cell adenocarcinoma and signet ring cell adenocarcinoma are rarer types. Transitional stages suggest the common origin of these tumors from mucus-secreting cylinder cells of the respiratory epithelium. The grade of differentiation and the tumor type are definitely related to the prognosis of these tumors. Similar to the tumors of the gastrointestinal tract, electron microscopy and immunohistochemistry prove the existence of a number of various polypeptide hormones, the significance of which has not yet been clarified.

Dynamics of arbuscule development and degeneration in mycorrhizas of Triticum aestivum L. and Avena sativa L. with reference to Zea mays L

Abstract: SUMMARY A quantitative light and electron microscope study of developing and degenerating arbuscules of the mycorrhizal fungus Glomus fasciculatum (Thax. sensu Gerd.) Gerd. & Trappe in Triticum aestivum L. (wheat) and Avena sativa L. (oats) was carried out in order to estimate three parameters during the colonization cycle and to compare these parameters to those in Zea mays L. The parameters are: (1) Vv (f,c), the fraction of the host cell volume (c) occupied by a volume of fungus (f); (2) Vv,(cy, c), the fraction of the host cell volume occupied by host cytoplasm (cy); (3) Sv(p,c) the surface area-to-volume ratio of the host protoplast (p) to the whole host cell. Uninfected cortical cells of wheat had an Sv,(p,c) of 0.11 μm2μm −3 and those of oats 0.10 μm2μm −3. As the fungus penetrates the cell wall, the protoplast invaginates, causing a decrease in protoplast volume and an increase in St. In wheat this increase reached 1.17 μm2μm−3 and in oats, 1.04 μm2μm−3. When the arbuscule is mature, the fungus occupies 35% of the cell in wheat with 20% as branches and 15% as trunk. In oats, the fungus occupies 36% of the cell, with 23 % as branches and 13 % as trunk. In wheat, host cell cytoplasm was initially 39 % and increased to 21.6% and in oats, from 3.6 to 28.8%. These values are similar to those observed in Zea mays. The rates at which the parameters Vv(f,c) and Sv(p,c) changed during arbuscule development and degeneration were similar. The amount of encasement and host cell cytoplasm showed the greatest variation among host species.

Characterization of two different genes (cDNA) for cytochrome c oxidase subunit VIa from heart and liver of the rat.

Abstract: By antibody screening of a rat liver and a rat heart cDNA library in lambda gt11 two clones coding for the liver- and heart-specific subunit VIa of rat cytochrome c oxidase were isolated. In the heart cDNA sequence a TAA stop codon was found in frame 18 bp 5' upstream of the first methionine codon, thus excluding a leader sequence for this protein. The two cDNAs contain the full-length coding region of two subunits. The amino acid sequences of the two subunits show only 50% homology, whereas 74% homology was found between rat heart and bovine heart subunit VIa. By Northern blot analysis it is shown that the gene for subunit VIa from heart is only expressed in heart and skeletal muscle, whereas that from liver is also expressed in kidney, brain, heart and weakly in muscle.

Seasonal acclimation of bank voles and wood mice: nonshivering thermogenesis and thermogenic properties of brown adipose tissue mitochondria.

Abstract: Seasonal acclimation of nonshivering thermogenesis and brown adipose tissue was studied in wild bank voles (Clethrionomys glareolus), yellow necked field mice and wood mice (Apodemus flavicollis, A. sylvaticus). Both, voles and mice increased their capacity for nonshivering thermogenesis during winter. Thermogenic properties of brown fat (cytochrome c oxidase activity, mitochondrial protein content, GDP-binding of brown fat mitochondria) showed similar changes during seasonal acclimation;Clethrionomys andApodemus spp. both showed lowest thermogenic properties in the summer during August, a rapid increase during fall, and highest levels of thermogenic activity in the winter months. With regard to changes in body weight and brown fat mass these species show different strategies for seasonal acclimation. InClethrionomys a reduction of body mass in the winter was found, both in the wild population as well as in individual animals housed in the laboratory.A. flavicollis showed a reduction of body weight during fall, whereasA. sylvaticus maintained a constant body mass throughout the year. Brown fat mass and cellularity increased in theApodemus spp. during winter, in parallel with the thermogenic properties of brown fat, whereas inClethrionomys brown fat mass and cellularity remained seasonally constant. These species live in the same habitat and were trapped in the same area. It is concluded that seasonal improvements of in vivo and in vitro thermogenesis are very similar in these species, although the physiological basis for this improvement is different inClethrionomys andApodemus.

The glycoprotein of influenza C virus is the haemagglutinin, esterase and fusion factor.

Abstract: Of the biological activities of influenza C virus, haemagglutination, receptor inactivation and fusion, only the latter has been conclusively correlated with its surface glycoprotein (gp). We have purified the gp by octylglucoside treatment of influenza C virions followed by centrifugation into a sucrose gradient. Evidence was obtained that gp also represents the receptor-destroying enzyme of influenza C virus, which has been characterized as a neuraminate 9-O-acetylesterase: (i) it inactivated the receptors for influenza C virus on chicken erythrocytes; (ii) it had acetylesterase activity as indicated by the release of acetate from bovine submandibulary mucin; (iii) monoclonal antibodies directed against gp inhibited the acetylesterase activity of influenza C virus. Although purified gp was unable to agglutinate chicken red blood cells, it blocked haemagglutination by viruses. This finding as well as the haemagglutination inhibition activity of monoclonal anti-gp antibodies indicate that gp is also responsible for the haemagglutinating activity of influenza C virus. Thus, as the influenza C glycoprotein is the only myxovirus glycoprotein with three different activities, we propose the designation HEF in order to describe its function as a haemagglutinin (H), an esterase (E) and a fusion factor (F).

New trends in photobiology the role of flavins as photoreceptors

Abstract: Almost every facet in the life of plants and fungi can be controlled by blue light. There are numerous blue-light responses with action spectra resembling the absorption spectra of flavoproteins. The photochemical properties of flavoproteins make them well suited for photoreception between 300 and 500 nm and potentially also beyond 500 nm. Evidence that flavoproteins act as blue-light photoreceptors comes in part from receptor substitution experiments with flavin analogues. Attempts to distinguish flavoproteins with photoreceptor function from bulk flavoproteins are also made by fluorescence lifetime measurements and analysis of light-induced absorbance changes that indicate cytochrome-b reduction. The only well-characterized and isolated flavin-type photoreceptors to date are the DNA photolyases of E. coli, yeast and Streptomyces.

Phenolic and mineral content of leaves influences decomposition in European forest ecosystems.

Abstract: Factors influencing decomposition in European forests growing on different soils were studied in stands dominated by the European beechFagus sylvatica L. Phenolic contents of freshly fallen leaves ofF. sylvatica growing on nutrient-poor soils (acid sandy soil) were higher than those of similar leaves on nutrient-rich soils (calcareous mull soil). Analysis of fallen leaves of different ages showed rapid decay of phenolics during the first winter on the ground. After 1 year the phenolic content of leaves ofF. sylvatica growing on nutrient-poor soils was still twice as high as in similar leaves on nutrient-rich soils. Field and laboratory experiments showed that a major decomposer (Oniscus asellus, Isopoda) preferred leaves from trees on nutrient-rich soils. Mineral contents of leaves ofF. sylvatica growing on different soils differed: on rich soils leaves had higher contents of Ca, Mg, Na, and K. These elements are important nutrients for decomposers. The distribution of major decomposers reflects the mineral content of their diet, which in turn reflects soil type. Different rates of leaf turnover and nutrient turnover in different forest ecosystems (even when the same tree species is dominant) are due to the decomposing system, which is influenced by the phenolic and mineral contents of the leaves.

Sociality in molerats : Metabolic scaling and the role of risk sensitivity.

Abstract: The foraging behaviour and diets of the various bathyergid molerat species are reviewed briefly, and inferences are drawn concerning their dietary specialisation. A simple model has been constructed which investigates the risks of unproductive foraging by specialist feeders as a function of resource dispersion characteristics and group size. The model suggests that the principal benefit of group foraging is a reduction in foraging risk, rather than increased resource procurement per se. Meeting the energetic costs of non-workers in social groups necessitates a reduction of the total energetic expenditure of the colony. This is achieved by reducing body size, huddling in the nest, and scaling mass-specific resting metabolic rate virtually independent of mass.

Molecular Basis of Infectivity and Pathogenicity of Newcastle Disease Virus

Abstract: Newcastle disease virus (NDV) can be isolated from a wide variety of different avian species. Differences in virus pathogenicity have been observed which depend on the host infected as well as on the virus strain involved. Chickens seem to be the most susceptible species. Ducks and geese, on the other hand, are reported to be refractory even to the most pathogenic viruses for chickens (27). There is evidence that adaptation of a particular NDV strain to a novel host may affect pathogenicity. Thus, Alexander and Parsons (1) reported that NDV isolates from pigeons required several passages in chickens, before their potential pathogenicity became manifest in this species. Although the reason for this host specificity of NDV is not known, such observations are of epidemiological significance. They explain how potentially pathogenic virus strains can be generated and maintained in a particular species without harm. This pathogenic potential could then become fully manifest when a different species of highly susceptible birds, such as chicken, is exposed to these viruses.