Evidence for a junctional feet-ryanodine receptor complex from sarcoplasmic reticulum

Heavy sarcoplasmic reticulum vesicles, labelled with the Ca2+ release channel probe [3H]ryanodine, were solubilized in detergent, then centrifuged through sucrose gradients. A single peak of ryanodine binding activity was observed with an apparent sedimentation coefficient of 30S. Electron microscopy of the peak fraction showed disk structures of 25-28 nm diameter and 10 nm thickness. Proteins specifically enriched in the peak fraction were the Mr 160,000 and 260,000 and junctional feet proteins (Mr 320,000 and 300,000). This suggests that the feet proteins and ryanodine receptor may be specifically associated into a large oligomeric complex comprising subunits of Mr 160,000-320,000.     

Lipopolysaccharides of Thiocystis violacea, Thiocapsa pfennigii, and Chromatium tepidum, species of the family Chromatiaceae.

The lipopolysaccharides (LPS) of three species of purple sulfur bacteria (Chromatiaceae), Thiocystis violacea, Thiocapsa pfennigii, and the moderately thermophilic bacterium Chromatium tepidum, were isolated. The LPS of Thiocystis violacea and Chromatium tepidum contained typical O-specific sugars, indicating O-chains. Long O-chains were confirmed for these species by sodium deoxycholate gel electrophoresis of their LPS. Thiocapsa pfennigii, however, had short or no O-chains. The core region of the LPS of all three species comprised D-glycero-D-mannoheptose as the only heptose and 2-keto-3-deoxyoctonate. The lipid A, obtained from the LPS by mild acid hydrolysis, contained glucosamine as the main amino sugar. Amide-bound 3-hydroxymyristic acid was the only hydroxy fatty acid. The main ester-bound fatty acid in all lipid A fractions was 12:0. Mannose and small amounts of 2,3-diamino-2,3-dideoxy-D-glucose were common constituents of the lipid A of the three Chromatiaceae species investigated. All lipid A fractions were essentially free of phosphate.     

Dibutyryl cyclic AMP triggers Ca2+ influx and Ca2+-dependent electrical activity in pancreatic B cells

In the presence of 7 mM glucose, dibutyryl cyclic AMP induced electrical activity in otherwise silent mouse pancreatic B cells. This activity was blocked by cobalt or D600, two inhibitors of Ca2+ influx. Under similar conditions, dibutyryl cyclic AMP stimulated 45Ca2+ influx (5-min uptake) in islet cells; this effect was abolished by cobalt and partially inhibited by D600. The nucleotide also accelerated 86Rb+ efflux from preloaded islets, did not modify glucose utilization and markedly increased insulin release. Its effects on release were inhibited by cobalt, but not by D600. These results show that insulin release can occur without electrical activity in B cells and suggest that cyclic AMP not only mobilizes intracellular Ca, but also facilitates Ca2+ influx in insulin secreting cells.     

Mapping of the variegate porphyria (VP) gene: Contradictory evidence for linkage between VP and microsatellite markers at chromosome 14q32

The gene for variegate porphyria (VP), an autosomal dominant disease with a high prevalence in South Africa, evidently due to a founder effect, was previously mapped to chromosome 14q32. In the current study this localization was evaluated by linkage and haplotype analyses using microsatellite markers spanning a region of more than 20 cM on chromosome 14q32. In many recent studies linkage disequilibrium between disease and marker loci has been utilized to map genes in founder populations, but we could not find any association between VP and the markers used in this study. Our data suggest that the allocation of VP to chromosome 14q32 may be incorrect. Received: 1 September 1995 / Revised: 1 November 1995