Energy flow and the vertical structure of real ecosystems

Summary Three possible explanations for the well-known limitation of food chain lengths to two or three links for the most part are subjected to an empirical test, using the fact that ectotherms, especially invertebrates, tend to have higher production efficiencies than endotherms. The data are consistent with the hypothesis that food chain lengths are limited by the availability of energy.     

Organization of the ribosomal ribonucleic acid genes in various wild-type strains and wild-collected strains of Neurospora

Summary The organization of the ribosomal DNA (rDNA) repcat unit in the standard wild-type strain of Neurospora crassa, 74-OR23-1A, and in 30 other wild-type strains and wild-collected strains of N. crassa, N. tetrasperma, N. sitophila, N. intermedia, and N. discreta isolated from nature, was investigated by restriction enzyme digestion of genomic DNA, and probing of the Southern-blotted DNA fragments with specific cloned pieces of the rDNA unit from 74-OR23-1A. The size of the rDNA unit in 74-OR23-1A was shown to be 9.20 kilobase pairs (kb) from blotting data, and the average for all strains was 9.11+0.21 kb; standard error=0.038; coefficient of variation (C.V.)=2.34%. These data indicate that the rDNA repeat unit size has been highly conserved among the Neurospora strains investigated. However, while all strains have a conserved HindIII site near the 5 end of the 25 S rDNA coding sequence, a polymorphism in the number and/or position of HindIII sites in the nontranscribed spacer region was found between strains. The 74-OR23-1A strain has two HindIII sites in the spacer, while others have from 0 to at least 3. This restriction site polymorphism is strain-specific and not species-specific. It was confirmed for some strains by restriction analysis of clones containing most of the rDNA repeat unit. The current restriction map of the 74-OR23-1A rDNA repeat unit is presented.     

The effect of ethanol on arachidonic acid metabolism in the murine peritoneal macrophage

Exposure to ethanol in man has been linked to an alteration of the immune surveillance system and reduced ability of the macrophage to undergo phagocytosis. Since ethanol has been suggested to alter membrane function and inhibit the production of calcium ionophore stimulated synthesis of prostaglandins and leukotrienes by the human neutrophil and transformed murine mast cell, the dose response effect of ethanol on the biosynthesis of icosanoids by the peritoneal macrophage during zymosan phagocytosis was studied. Peritoneal macrophages from two inbred strains of mice derived from a common stock (HS) and selected for sensitivity to ethanol (shoprt sleep [SS]/long sleep [LS]) were studies. Zymosan phagocytosis was found to lead to synthesis of LTC₄ (70 ng/10⁶ cells), 6-keto-PGF_1a (5 ng/10⁶ (3 ng/10⁶ cells). For the HS macrophage, ethanol caused a dose dependent inhibition of these lipid mediators as well as inhibition of phagocytosis and release of beta-hexosaminidase. However, a difference was observed in arachidonate metabolism stimulated by phagocytosis between the LS and SS mice below 100 mM ethanol. The SS mouse had a 50% inhibition of cyclooxygenase products at 86 mM ethanol with no inhibition of lipoxygenase metabolites. The LS mice had a trend suggesting increased lipoxygenase metabolites below 100 mM ethanol. At these levels of ethanol which can be found in man, these results suggest there may be differential production of lipid mediators under genetic control.     

Efficient degradationin vitro of all intermediate filament subunit proteins by the Ca2+-activated neutral thiol proteinase from Ehrlich ascites tumor cells and porcine kidney

Vimentin, desmin, glial fibrillary acidic protein, neurofilament triplet proteins, and a mixture of cytokeratins were digested with Ca²⁺-activated neutral thiol proteinase isolated from Ehrlich ascites tumor (EAT) cells and porcine kidney. All intermediate filament proteins were degraded by the proteinase, although with different rates and Ca²⁺ optima. These results are in part at variance with our previous statement that the Ca²⁺-activated proteinase from EAT cells is specific for vimentin and desmin.     

Enzymes metabolizing dimethylamine, trimethylamine and trimethylamine N-oxide in the yeast Sporopachydermia cereana grown on amines as sole nitrogen source

Abstract Sporopachydermia cereana , an ascosporogenous yeast, grew on dimethylamine, trimethylamine or trimethylamine N -oxide as sole nitrogen sources and produced mono-oxygenases for dimethylamine and trimethylamine that were significantly more stable than the corresponding enzymes found in Candida utilis . No trimethylamine mono-oxygenase activity was found in S. cereana grown on dimethylamine. In cells grown on trimethylamine N -oxide (but not on the other nitrogen sources), evidence for an enzyme metabolizing the N -oxide, possibly an aldolase, but more probably a reductase was obtained. All these activities showed a similar requirement for the presence of FAD or FMN in the extract buffer during isolation to retain activity. Amine mono-oxygenase activities showed a similar sensitivity to inhibitors, including proadifen hydrochloride and carbon monoxide as the corresponding enzymes in C. utilis . The trimethylamine N -oxide-dependent oxidation of NADH was more sensitive to inhibition by EDTA, N -ethylmaleimide and β-phenylethylamine than the mono-oxygenases, and less sensitive to KCN, and activity was significantly higher with NADPH than was observed with the 2 mono-oxygenases.     

Surface-charge related actions of polylysine on thylakoid membranes

Polycation binding to the negatively charged surface of chloroplast thylakoid membranes is known to cause an inhibition of photosystem I activity. It also interferes with the cation-dependent rearrangement of chlorophyll proteins in the thylakoid membrane. It was shown that added anions prevented or reversed the inhibition of photosystem I by polylysine without decreasing its binding to the membranes. Anions also caused a change in the interaction of the chlorophyll proteins in polylysine-treated thylakoids as indicated by an increase in the relative fluorescence intensity from photosystem II. In both cases, the relative effectiveness of the anions tested depended on their valence; for example, the tetravalent species Fe(CN)₆^4t- was effective at a concentration at least 2 orders of magnitude lower than the divalent species SO₄^2?. These results suggest that anions act by screening the positive charge of the polylysine-coated membrane surface. Measurements of the response of the anionic fluorescent probe 1-anilinonapthalene-8-sulfonate to an addition of anions to polylysine-treated thylakoids supported this contention. It was concluded that the action of polylysine on photosystem I and on the chlorophyll proteins is mediated by changes of the electrical properties of the thylakoid membrane and may not involve a direct binding of the polycation to the affected membrane proteins.     

Stochastic models for cell kinetics

A survey is given of branching process type methods in cell kinetics. Some results are given that allow circadian rhythm and do not require complete independence between cells. Some more classical results on balanced exponential growth are given and some comments are made on flow microfluorometry.     

Haemolysis of rabbit erythrocytes by a lectin from the seeds of<Emphasis Type="Italic">Croton tiglium</Emphasis>

The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K⁺, Ca²⁺ and Mg²⁺ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.     

Plant lectins specific for N-acetyl-β-D-galactosamine

N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).