Acceleration of surface-dependent autocatalytic activation of blood coagulation factor XII by divalent metal ions

The effect of divalent metal ions on the rate of dextran sulfate dependent autocatalytic activation of human blood coagulation factor XII was studied at pH 7.4 and 25 degrees C. Zn2+ and Cu2+, but not Co2+, increased the rate of factor XII activation induced by dextran sulfate with optimum effects at approximately 5 and 1 microM, respectively, while Ca2+ acceleration required much higher concentrations (millimolar). Further investigation of the effect of Zn2+ on factor XII activation demonstrated a complete dependence on the presence of dextran sulfate, lack of inhibition by soybean trypsin inhibitor, the appearance of alpha-XIIa as the primary reaction product, and reaction kinetics characteristic of an autocatalytic process. These results were consistent with Zn2+ affecting only the rate of surface-mediated factor XII autoactivation. The initial turnover velocity of dextran sulfate induced factor XII autoactivation increased linearly with factor XII concentration in the absence of Zn2+ up to 0.9 microM factor XII but showed saturation behavior over this same concentration range in the presence of 5 microM Zn2+, indicating that Zn2+ increased the reaction rate primarily by lowering the apparent Km. Comparison of the kinetics of autoactivation at mu = 0.15 and 0.24 revealed that the enhancement in the apparent kcat/Km brought about by Zn2+ increased from 19-fold to 520-fold, respectively, due to a differential dependence of the Zn2+-stimulated and unstimulated reactions on ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth of Nitrobacter by dissimilatoric nitrate reduction

Abstract Eight strains of the genus Nitrobacter grew under anaerobic conditions in the presence of nitrate. The growth was inhibited by nitrate concentrations above 0.5 mM. By a special culture technique inhibition caused by nitrite was abolished. Nitrate oxidizing cells grew in gas tight culture flasks as a biofilm on a gas-permeable silicone tubing. The biofilm allowed nitrate-reducing cells to grow at a low nitrite concentration. These cells grew either actively motile in the anaerobic medium, or in anaerobic zones of the biofilm. They produced nitrite and ammonia. Nitrogen balance calculations established a loss of inorganic nitrogen for 5 of 8 strains. This implies that nitrate-reducing cells produced furthermore volatile nitrogen compounds. N₂O was detected by gas chromatography.     

Response of grasshoppers (Orthoptera: Acrididae) to livestock grazing in southeastern Arizona: differences between seasons and subfamilies

Summary Grasshopper densities were compared between grazed and ungrazed semidesert grassland sites in southeastern Arizona. Bouteloua-dominated perennial grass cover was about 1.5 times greater on the livestock exclosure. Grasshoppers were 3.7 times more abundant on the protected area in the summers of 1983 and 1984, when dominant species were grass-feeding members of the subfamily Gomphocerinae. In fall 1984, grasshoppers were 3.8 times more common on the grazed site, when dominants were mainly herb-feeders in the subfamily Melanoplinae. These results indicate important seasonal and taxonomic differences in the responses of grasshoppers to the activities of vertebrate grazers.     

Mechanism and binding specificity of beta-glucosidase-catalyzed hydrolysis of cellobiose analogues studied by competition enzyme kinetics monitored by 1H-NMR spectroscopy

The application of high-resolution 1H-NMR spectroscopy to monitor substrate and product time dependencies in progress curve enzyme kinetics is described with beta-glucosidase-catalyzed hydrolyses of cellobiose analogues as examples. It is demonstrated that inhibition patterns, relative binding specificities and catalytic rates can be inferred from competition experiments with two or more substrates. It could be concluded from competition experiments that substrates which form less stable enzyme-substrate complexes than methyl beta-cellobioside are hydrolyzed faster than this reference substrate when they are the sole substrate, due to a lower activation energy in the catalytic step, but that they are hydrolyzed slower than the reference compound in direct competition, due to the formation of the less stable enzyme-substrate complex in the binding step.     

A new facultatively nitrite oxidizing bacterium,Nitrobacter vulgaris sp. nov.

A total of 17 facultatively lithoautotrophic strains of Nitrobacter were investigated. They all were found to be related on the species level by DNA hybridizations. The G+C content of DNA ranged between 58.9 and 59.9 mol %. The isolates originated from divers environments. The cells were 0.5–0.8×1.2–2.0 m in size and motile by one polar to subpolar flagellum. Cell-division normally occurred by budding. Polar caps of intracytoplasmic membranes as well as carboxysomes were present. The cells tended to excrete extracellular polymers forming aggregates or biofilms. Heterotrophic growth was slower than mixotrophic but often faster than litoautotrophic growth. In the presence of nitrite and organic substances the organisms often showed diphasic growth. First nitrite and then the organic material was oxidized. In the absence of oxygen growth was possible by dissimilatory nitrate reduction. Nitrite, nitric and nitrous oxide as well as ammonia were formed. Depending on growth conditions the generation times varied from 12 to 140 h. The new Nitrobacter spec. may be one of the most abundant nitrite-oxidizing bacteria in soils, fresh waters and natural as well as artificial stones. For this organism the name Nitrobacter vulgaris is proposed.The type strain is filed with the culture collection of the Institut für Allgemeine Botanik, Universität Hamburg, FRG.     

Comparison of 16S rRNA sequences from the family Pasteurellaceae: phylogenetic relatedness by cluster analysis

The taxonomy of the family Pasteurellaceae has remained controversial despite investigations of biochemistry, serology, and nucleic acid relatedness. In an attempt to resolve some of this confusion, we have partially sequenced the 16S rRNAs of seven members of the family, representing all three genera. The sequences were aligned, similarity scores calculated, and single, average and complete linkage cluster analysis of the resulting distance matrix performed. In this way, an evolutionary branching pattern of these closely related species was reconstructed, and the approximate phylogenetic position of the family determined. Actinobacillus (Haemophilus) actinomycetemcomitans clustered with Haemophilus instead of Actinobacillus, supporting transfer of this species to the genus Haemophilus. Thus cluster analysis of phylogenetic relatedness was found to be particularly useful for studying closely related organisms, and could be performed using a microcomputer.     

Serotonin content of rabbit lung and small intestine during perinatal development

Serotonin (5-hydroxytryptamine, or 5HT) was measured in extracts of rabbit lung and intestine during perinatal development using high pressure liquid chromatography (HPLC) with electrochemical detection. Lung and intestine were extracted with HClo4 and the extract was loaded onto a Bio-Rex 70 resin column. After elution with acetic acid the samples were injected onto the HPLC column. Serotonin was detected in lung and intestine at 18 days of gestation (80 and 90 ng/mg protein). In lung serotonin content increased at day 28 (290 ng/mg protein) till day 30 (680 ng/mg protein) decreased at day 1 after birth (480 ng/mg protein) and then rose at day 10 of the newborn period (650 ng/mg protein). In intestine the serotonin content was always higher than in the lung. At the end of gestation the serotonin in the intestine remained constant (2410 ng/mg protein at day 28 and 2430 ng/mg protein at day 30), decreased slightly one day after birth (2150 ng/mg protein) and rose at day 10 (3300 ng/mg protein).     

Biosynthesis of the neural cell adhesion molecule: characterization of polypeptide C

The biosynthesis of the neural cell adhesion molecule (N-CAM) was studied in primary cultures of rat cerebral glial cells, cerebellar granule neurons, and skeletal muscle cells. The three cell types produced different N-CAM polypeptide patterns. Glial cells synthesized a 135,000 Mr polypeptide B and a 115,000 Mr polypeptide C, whereas neurons expressed a 200,000 Mr polypeptide A as well as polypeptide B. Skeletal muscle cells produced polypeptide B. The polypeptides synthesized by the three cell types were immunochemically identical. The membrane association of polypeptide C was investigated with methods that distinguish peripheral and integral membrane proteins. Polypeptide C was found to be a peripheral membrane protein, whereas polypeptides A and B were integral membrane proteins with cytoplasmic domains of approximately 50,000 and approximately 25,000 Mr, respectively. The affinity of the membrane binding of polypeptide C increased during postnatal development. The posttranslational modifications of polypeptide C were investigated in glial cell cultures, and it was found to be N-linked glycosylated and sulfated.