Order-disorder phase transition and lipid dynamics in rabbit small intestinal brush border membranes. Effect of proteins

The total lipids extracted from brush border membranes form smectic lamellar phases when dispersed in water. 31P broad-band nuclear magnetic resonance (NMR) shows that between body temperature (37 degrees C) and freezing of the solvent, the extracted lipids form bilayers with the lipid molecules undergoing fast anisotropic motion. This is also true for the lipids present in the brush border membrane. The electron spin resonance (ESR) results obtained with various hydrophobic spin probes incorporated in either brush border vesicle membranes or their extracted lipids are consistent with this interpretation. By use of a variety of chemically different spin-labels, the temperature dependence of brush border membranes and their extracted lipids was probed. The temperature dependence of various ESR spectral parameters shows discontinuities that, by comparison with differential scanning calorimetry, are assigned to a lipid thermotropic phase transition. Differential scanning calorimetry shows that the lipid in brush border membranes undergoes a broad, reversible phase transition of low enthalpy between 10 and 30 degrees C, with a peak temperature of about 25 degrees C. Hence, the brush border membrane of rabbit small intestine functions in the liquid-crystalline state, well above the peak temperature and also above the upper limit of the lipid phase transition. Therefore, in itself, the thermotropic lipid phase transition is unlikely to play a physiological role. The low enthalpy of the lipid phase transition, indicative of a lack of cooperativity, is primarily attributed to the relatively high cholesterol content and to heterogeneity in the lipid composition of this membrane [Hauser, H., Howell, K., Dawson, R. M. C., & Bowyer, D. E. (1980) Biochim. Biophys. Acta 602, 567-577].(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimation of pyruvate decarboxylation in perfused rat skeletal muscle

A total of 46 E. coli strains showing mannose-resistant, P-blood-group independent hemagglutination of human erythrocytes were tested for binding to neuraminic acid. Nine of the strains completely lost their hemagglutination activity after the erythrocytes were treated with neuraminidase. To characterize the receptor structure, different neuraminic acid containing glycoproteins, their desialylated derivatives and neuraminyl oligosaccharides were tested for hemagglutination inhibition. These studies showed that the nine strains had binding specificity for alpha 2-3 linked neuraminic acid.     

Molecular forms of beta-hexosaminidase and cathepsin D in serum and urine of healthy subjects and patients with elevated activity of lysosomal enzymes.

A procedure is described that allows the characterization of the molecular forms of beta-hexosaminidase and cathepsin D in controls and pathological specimens of human serum and human urine. The following observations were made. (1) In human serum, beta-hexosaminidase (alpha- and beta-chain) and cathepsin D are present predominantly in their high-molecular-weight precursor forms. In human urine, these enzymes exist as both precursor and mature forms. (2) Cathepsin D precursor from serum and urine differs in the number of oligosaccharides that are sensitive to endo-beta-N-acetylglucosaminidase H. Therefore the urine enzyme is not likely to originate from the serum. (3) The presence exclusively of precursors of beta-hexosaminidase and of cathepsin D in the sera of patients with hepatitis suggests that in hepatitis secretion of lysosomal enzymes is elevated, rather than the enzymes leaking from damaged cells. (4) In the urine of patients with nephrotic syndrome, beta-hexosaminidase and cathepsin D are present in grossly elevated amounts, but do not differ in the polypeptide patterns from controls. (5) In urine from a patient with mucolipidosis II, the elevated activity of beta-hexosaminidase is accounted for mainly by the precursor forms. Mature beta-chain of beta-hexosaminidase is lacking, and incompletely processed beta-hexosaminidase polypeptides are present. Both the precursor and the mature forms of cathepsin D are increased. They contain only complex oligosaccharides.     

Coding and 3' non-coding nucleotide sequence of chalcone synthase mRNA and assignment of amino acid sequence of the enzyme

The nucleotide sequence of an almost complete cDNA copy of chalcone synthase mRNA from cultured parsley cells (Petroselinum hortense) has been determined. The cDNA copy comprised the complete coding sequence for chalcone synthase, a short A-rich stretch of the 5' non-coding region and the complete 3' non-coding region including a poly(A) tail. The amino acid sequence deduced from the nucleotide sequence of the cDNA is consistent with a partial N-terminal sequence analysis, the total amino acid composition, the cyanogen bromide cleavage pattern, and the apparent mol. wt. of the subunit of the purified enzyme.     

Simian virus 40 and polyoma virus induce synthesis of heat shock proteins in permissive cells.

During the lytic infection of monkey and mouse cells with simian virus 40 and polyoma virus, respectively, the preferentially increased synthesis of two host proteins of 92,000 and 72,000 Mr was observed by 15 to 20 h after infection besides the general stimulation of most cellular proteins. The incubation of uninfected monkey and mouse cell cultures for 30 to 60 min at 43.5 degrees C induced the enhanced synthesis of at least three proteins of 92,000, 72,000 and 70,000 Mr, the last one being the major heat shock protein of mammalian cells. Two-dimensional gel electrophoresis and partial proteolytic digestion confirmed that the same 92,000- and 72,000-Mr proteins are stimulated by virus infection and thermal treatment. In simian virus 40-infected CV-1 cells, we also observed the weak stimulation of a 70,000-Mr protein comigrating in gel electrophoresis with the major heat shock protein. The 92,000-, 72,000- and 70,000-Mr proteins of monkey cells are structurally very similar to the corresponding proteins of mouse cells. In immunoprecipitations, no specific association of these proteins to simian virus 40 T antigens was noticed.     

Nucleotide pools of growing,synchronized and stressed cultures of Saccharomyces cerevisiae

High pressure liquid chromatography has been used to study the acid soluble nucleotide pool of Saccharomyces cerevisiae under different conditions of growth. ATP, ADP, AMP, NAD, GTP, UTP, UDP, CTP, CDP, and UDP-sugars plus UMP could be separated and were found in concentrations higher than 0.1 mumol per g yeast cell dry weight (= detection limit). During glucose-limited continuous culture the levels of individual nucleotides depended on the growth rate, which was most pronounced with pyrimidine (uridine, cytidine) nucleotides. The energy charge (E.C.) remained high (0.9) at all growth rates (0.07-0.3 h-1). During synchronized growth at a constant growth rate (0.11 h-1) almost all nucleotide levels and the E.C. remained at constant values with the only exception of UDP-sugars and UMP of which increased levels were found during the phase of budding. Under conditions of metabolic stress (addition of antimycin A, deoxyglucose plus iodoacetate) pronounced changes in the levels of purine (adenine and guanine) nucleotides and the E.C. were observed. All other nucleotides were less influenced by these conditions. Only under these conditions IMP accumulation was observed. The results strongly argue against the significance of purine nucleotide or E.C. measurements under viable conditions. In contrast, changes in the levels of pyrimidine nucleotides seem to be indicative of changes in the flux through the metabolic pathways where they act as coenzymes.     

Nonlinear analysis of some models for the evolution of dominance

For two different classes of models for the evolution of dominance modifiers a nonlinear analysis is performed. The first class arises from the classical model of R. A. Fisher by assuming that the modifiers under consideration are not neutral in their pleiotropic effects. The second class is based on a model of P. M. Sheppard for the evolution of dominance in mimicry. Again the derived models with non-neutral modifiers are analysed.