Does interference competition from Daphnia affect populations of Keratella cochlearis in Loch Leven, Scotland?

A very marked inverse relationship between Daphnia hyalina var.lacustris Sars and Keratella cochlearis (Gosse) population densitieswas observed in Loch Leven, Scotland, UK between 1978 and 1982.The natural death rates of the rotifer population were far lowerthan would have been expected in response to interference competitionfrom Daphnia. Keratella birth rates fell, along with chlorophylla concentrations, when Daphnia filtration rates were high. Theresults indicate that, when Daphnia were abundant, direct competitionfor food was the most likely factor suppressing Keratella populationgrowth.     

Sequence divergence and open regions of RNA secondary structures in the envelope regions of the 17 human immunodeficiency virus isolates.

Genetic variation during the course of infection of an individual is a remarkable feature of the acquired immune deficiency syndrome (AIDS) disease. This variation has been studied for the envelope protein encoding regions of seventeen different sequences from various isolates of human immunodeficiency virus (HIV) using multiple sequence comparison and calculation of variability. The open regions with little intramolecular base pairing in these envelope sequences are predicted by a recently developed statistical method. The minimum length L for a run of hypervariable sites, conserved sites, or open regions that gives significance at the 1% (or 0.1%) level is then determined by a scan statistical method. The results show that significant clusters of open regions predicted at the RNA levels correlate with significant clusters of hypervariable sites in the HIV envelope gene. Those significant genomic variations in HIVs seem to be manifested mainly in the extracellular portion of the envelope protein. Twelve potential antigenic determinants are predicted using an antigenic index method. Interestingly, the majority of the significant hypervariable regions in the exterior envelope protein (gp120) were predicted potential epitopes.     

Purification and properties of the DNA-binding protein HPB12 from Bacillus subtilis nucleoid

We report the purification to homogeneity of a 12 KDa protein (HPB12) present in the nucleoids of Bacillus subtilis. From the purification data the abundance of the protein was estimated to about 20,000 monomers per cell. The HPB12 protein is heat-stable and acid-soluble and binds preferentially to supercoiled and linearized double-stranded DNAs. The binding of the protein to the supercoiled DNA occurs very rapidly and appears to be cooperative. Moreover, the complexes are extremely stable and do not dissociate after 90 min. These properties are consistent with a role of the HPB12 protein in the structure of the B. subtilis chromosome.     

Permeability of human granulocytes to dimethyl sulfoxide

The permeability of the membrane of human granulocytes to the permeating solute dimethyl sulfoxide (DMSO) was studied using the Onsager form of the phenomenological equations derived from the theory of irreversible thermodynamics. Changes in cellular volume were monitored with an electronic particle counter as samples of that population were introduced into hypertonic osmotica. Temperature and concentration sensitivity analyses of the permeability coefficients were carried out. It is shown that the introduction of the Onsager formalism allows further insight into the observed transport phenomena. It was found that DMSO may affect the water permeability properties of the membrane for that population of cells.     

Pathophysiological variations in the rat liver plasma membrane serine proteinase activity

The effects of fasting, diabetes, cholestasis, two-third hepatectomy and adrenalectomy on the rat liver plasma membrane serine proteinase activity were studied. Our results show a significant decrease of the enzyme activity during fasting (-50%), during experimental diabetes (-50%), in regenerating liver after partial hepatectomy (-70%) and after extrahepatic cholestasis (-70%). No modifications are noted when the rats are bilaterally adrenalectomized. These findings suggest that the enzyme activity may be linked to the level of circulating insulin, and may be regulated in physiological cellular proliferation so as to prevent undesirable protein degradation.     

N-succinimidyl methoxyphenylacetic acid ester, an amine-directed chiral derivatizing reagent suitable for enzymatic scale resolutions

A chiral derivatizing reagent, N-succinimidyl-2-(S)-methoxy-2-phenylacetic acid ester (SMPA), directed toward reaction with primary amine-containing compounds has been synthesized and characterized. This reagent is suitable for HPLC resolution from enzymatic-scale reactions where only microgram quantities of chiral products may be obtainable. SMPA derivatization was shown to be effective in the resolution of the enantiomers of a number of different racemic compounds. SMPA was used to resolve the diastereoisomeric derivatives of a previously unknown enzymatically oxygenated product, allowing determination of the stereochemical course of the enzymatic reaction. SMPA is easily prepared from an inexpensive, commercially available, and enantiomerically pure precursor with the formation of a shelf-stable crystalline product which is utilizable in water-containing solutions. In addition to its usefulness for micro-determinations, SMPA is useful for preparative-scale resolutions of enantiomers since the reagent is cleaved from the diastereoisomeric derivative by acid hydrolysis.     

Instability of orthophthalaldehyde reagent for amino acid analysis

Determination of amino acids by reversed-phase chromatography of the adduct with orthophthalaldehyde and a thiol is rapid and sensitive. The major recognized adverse feature of this method is the instability of the reaction product, which requires precise control of reaction timing and chromatographic parameters for reliable quantitative application. We report another source of major variability: reagent instability. Deterioration of reagent was noted as low peak heights and peak broadening and was predictable if the premixed reagent was left at room temperature. Restoration of sharp chromatograms was accomplished by addition of mercaptoethanol or sodium metabisulfite. Reagent which was chromatographically inert contained minimal free thiol by direct assay. Free thiol disappearance was markedly slowed by addition of a chelating agent. Excess mercaptoethanol was deleterious. We conclude that reagent deterioration represents oxidation of the thiol, may be reversed by rereduction with minimal thiol or bisulfite, and may be minimized by inclusion of a metal chelator in the reagent.     

Effects of acetylene on hydrogenases from the sulfate reducing and methanogenic bacteria

The effect of acetylene on the activity of the three types of hydrogenase from the anaerobic sulfate reducing bacteria has been investigated. The (Fe) hydrogenase is resistant to inhibition by acetylene while the nickel-containing hydrogenases are inhibited by acetylene with the (NiFe) hydrogenase being 10-50 fold more sensitive than the (NiFeSe) hydrogenase. In addition the Ni(III) EPR signal (g approximately 2.3) of the "as isolated" (NiFe) hydrogenase was significantly decreased in intensity upon exposure to acetylene.