Phase variations inBifidobacterium animalis

Strains isolated from rabbit, chicken, and rat feces and from sewage and fermented milk products, all identified asBifidobacterium animalis, were found to show phase variations in colony appearance and in cellular morphology. The rate of transition in a switching system from opaque to transparent colonies and vice versa was determined. Differences in protein components and in penicillin-binding proteins (PBPs) of the cells from different colony types are shown.     

Subtelomeric expression regions of Borrelia hermsii linear plasmids are highly polymorphic

Borrelia hermsii, a relapsing fever agent, undergoes multiphasic antigenic variation to evade its host's immune response. Serotype specificity is determined by variable membrane lipoproteins, Vmps, which are expressed from genes located near the end of a linear plasmid. Using the polymerase chain reaction and primers representing the promoter of the active vmp and a conserved telomeric sequence, we characterized the subtelomeric expression regions of the 25 known serotypes of strain HS1. The distance from the promoter to the telomere fell into three size classes of approximately 1.0, 1.5, and 2.5 kilobases. In the sequenced serotypes the size differences were accounted for by variable lengths of the vmp genes and intervening sequences between 3' end of the vmp gene and the start of a downstream homology block. The degree of nucleotide identity between different vmp genes, or between the different 3' flanking DNA varied from 39-78%. Thus, there is length and sequence variability not only between vmp genes themselves but also between the 3' flanking regions of vmp genes.     

Effects of prolonged sodium restriction on the morphology and function of rat adrenocortical autotransplants

Summary Regenerated adrenocortical nodules were obtained by implanting fragments of the capsular tissue of excised adrenal glands into the musculus gracilis of rats (Belloni et al. 1990). Five months after the operation, operated rats showed a normal basal blood level of corticosterone, but a very low concentration of circulating aldosterone associated with a slightly increased plasma renin activity (PRA). Regenerated nodules were well encapsulated and some septa extended into the parenchyma from the connective-tissue capsule. The majority of parenchymal cells were similar to those of the zonae fasciculata and reticularis of the normal adrenal gland, while zona glomerulosa-like cells were exclusively located around septa (juxta-septal zone; JZ). In vitro studies demonstrated that nodules were functioning as far as glucocorticoid production was concerned, while mineralocorticoid yield was very low. Prolonged sodium restriction significantly increased PRA and plasma aldosterone concentration, and provoked a marked hypertrophy of JZ, which was due to increases in both the number and average volume of JZ cells. Accordingly, the in vitro basal production of aldosterone and other 18-hydroxylated steroids was notably enhanced. The plasma level of corticosterone, as well as zona fasciculata/reticularis-like cells and in vitro production of glucocorticoids by regenerated nodules were not affected. These findings, indicating that autotransplanted adrenocortical nodules respond to a prolonged sodium restriction similar to the normal adrenal glands, suggest that the relative deficit in mineralocorticoid production is not due to an intrinsic defect of the zona glomerulosa-like JZ, but is probably caused by the impairment of its adequate stimulation under basal conditions. The hypothesis is advanced that the lack of splanchnic nerve supply and chromaffin medullary tissue in regenerated nodules may be the cause of such an impairment.     

Lipid and lipoprotein metabolism in Hep G2 cells

Lipid composition, lipid synthesis and lipoprotein secretion by the Hep G2 cell line have been studied with substrate and insulin supplied under different conditions. The lipid composition of Hep G2 cells was close to that of normal human liver, except for a higher content in sphingomyelin (P less than 0.005) and a lower phosphatidylcholine/sphingomyelin ratio. Most of the [14C]triacylglycerols secreted into the medium were recovered by ultracentrifugation at densities of 1.006 to 1.020 g/ml. The main apolipoproteins secreted were apo B-100 and apo A-I. Hep G2 mRNA synthesized in vitro the pro-apolipoproteins A-I and E. Triacylglycerol secretion was 7.38 +/- 1.04 micrograms/mg cell protein per 20 h with 5.5 mM glucose in the medium and increased linearly with glucose concentration. Oleic acid (1 mM) increased the incorporation of [3H]glycerol into the medium and cell triacylglycerols by 251 and 899%, with a concomitant increment in cell triacylglycerols and cholesterol ester. Insulin (1 mU or 7 pmol/ml) inhibited triacylglycerol secretion and [35S]methionine incorporation into secreted protein by 47 and 28%, respectively, with a corresponding increase in the cells. Preincubation of cells with 2.5-10 mM mevalonolactone decreased the incorporation of [14C]acetate into cholesterol 6.2-fold, indicating an inhibitory effect on HMG-CoA reductase. It is concluded that in spite of some differences between Hep G2 and normal human hepatocytes, this line offers an alternative and reliable model for studies on liver lipid metabolism.     

The effect of Cyanophyta upon zooplankton in a eutrophic tropical lake (Lake Valencia,Venezuela)

The effect which Cyanophyta have upon the zooplankton varies according to the form of the alga (mucilaginous colonies or filaments) and its abundance. Periodical blooms of Microcystis aeruginosa were not detrimental for the zooplankton, in spite of the fact that copepods, cladocerans and rotifers consume small colonies. High concentrations of Lyngbya limnetica and Oscillatoria limnetica in Lake Valencia, Venezuela, proved to be inhibitory for cladocerans. A total absence of cladocerans was detected when filaments increased.     

Characterization and Biosynthesis of Cyclic-AMP-Binding Proteins in the Rat Central Nervous System

Cyclic-AMP-binding proteins in membrane and soluble fractions from rat forebrain were compared; membrane fractions included smooth and rough microsomes and a plasma membrane fraction enriched in synaptic membranes. Protein fractions were treated with 8-azido-[32P]cyclic AMP and ultraviolet irradiation to covalently tag cyclic-AMP-binding proteins. Labeled proteins were then analyzed by two-dimensional gel electrophoresis (2DGE) and fluorography. The soluble CNS proteins contained two major cyclic-AMP-binding species at 48K (48K 5.5 and 48K 5.45), differing slightly in their isoelectric points. Another protein was seen at 54K (54K 5.3) adjacent to the beta-tubulin subunits in the 2D electrophoretogram. The analysis of the smooth microsome and plasma membrane fractions differed from the soluble fraction in that there were two cyclic-AMP-binding proteins adjacent to the beta-tubulin region (54K 5.3 and 52K 5.3) differing slightly in apparent molecular weight. The membrane fractions also contained a cyclic-AMP-binding protein at 54K 5.8. The 52K 5.3 and 54K 5.8 species were unique to the membrane fractions. The rough microsomes did not contain detectable amounts of cyclic-AMP-binding proteins. Free polysomes were isolated from brain tissue, and translation products were analyzed by cyclic AMP affinity chromatography and immunopurification with antibodies to the brain specific type II regulatory subunit. The translation products that were found to bind cyclic AMP Sepharose are as follows: 48K 5.5, 48K 5.45, 52K 5.3, and 54K 5.8. These species comigrated with proteins that were photoaffinity-labeled in cytosol and membrane fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structural investigation of the capsular polysaccharide produced by a novel Klebsiella serotype (SK1). Location of O-acetyl substituents using NMR and MS techniques

The capsular polysaccharide of Klebsiella SK1 was investigated by methylation analysis, Smith degradation, and ¹H NMR spectroscopy. The oligosaccharides (P1 and P2) obtained by bacteriophage ΦSK1 degradation of the polymer were studied by methylation analysis, and 1D- and 2D-NMR spectroscopy. The resulting data showed that the patent repeating unit is a branched pentasaccharide having a structure identical to the revised structure recently proposed for Klebsiella serotype K8 capsular polysaccharide.

The 2D-NMR data showed that one third of the glucuronic acid residues in the SK1 polymer are acetylated at O-2, O-3, or O-4. FABMS studies confirmed the presence of monoacetylated glucuronic acid residues. Thus, the relationship between the Klebsiella K8 and SK1 polymers is akin to that found for Klebsiella polysaccharides K30 and K33, which have been typed as serologically distinct yet their structures differ only in the degree of acetylation.     

Crystallization and preliminary X-ray data of human plasma retinol-binding protein

Crystals of human plasma retinol-binding protein have been obtained from 4.5 m-NaCl buffered at pH 6.8 with 20 mm-cacodylate. The crystals are trigonal with space group R3 and unit cell dimensions, referred to the hexagonal system. $\text{a = b = 104.2}\text{A}\text{?}\text{and}\text{c = 74.5}\text{A}\text{?}$. The crystals diffract to a resolution of 2.0 Å.