Molecular organization in bacterial cell membranes. IV. Isolation by preparative electrophoresis in sodium dodecylsulphate and properties of the two major polypeptide groups of a "soluble" fraction from Streptomyces albus membranes

Mannose incorporation and lectin recognition of pronase-sensitive components in Micrococcus lysodeikticus (M. luteus) membranes

Isolated cytoplasmic membranes from Micrococcus lysodeikticus were able to incorporate [14C]mannose from GDP-[14C]mannose. Labelled mannose remained in the membrane fraction after its repeated washing and lipid extraction. Sodium dodecyl sulfate gel electrophoresis in 12% acrylamide showed a set of bands with molecular weights ranging from 230 000 to 19 000 which stained for protein and carbohydrate, and incorporated [14C]mannose. Some of these bands reacted with different lectins (concanavalin A, wheat germ agglutinin and ricin). Furthermore, the mannose was incorporated via a glycosylation pathway similar to that followed in eukaryotic system as shown by the preliminary identification of a lipid intermediate transferring the sugar to proteins and by the differential sensitivity to bacitracin and tunicamycin. These complex membrane components were sensitive to digestion with pronase. All the results presented suggest their glycoprotein nature.

Molecular organization in bacterial cell membranes. Sulfhydryl groups and disulfide bridges in Streptomyces albus and Escherichia coli K 12 cytoplasmic membranes

Plasma membranes from Streptomyces albus had 5.2 mol of sulfhydryl groups and 6 mol of disulfide bridges/50 kg proteins whereas Escherichia coli membranes had 3.4 mol sulfhydryl groups and 4 mol disulfide bridges/50 kg protein. About 66% of the sulfhydryl groups of S. albus membranes and 22% of those of E. coli membranes were readily accessible to titration with 5,5'-dithiobis(2-dinitrobenzoic acid). o-[3 Hydroxymercuri-2-methoxypropyl)-carbamyl]-phenoxyacetic acid (mersalyc acid) and p-chloromercuribenzoate were effective in solubilizing membrane proteins from the two bacteria. Other sulfhydryl group reagents, such as N-ethylmaleimide, iodoacetamide and iodoacetic acid, were less effective. Dithiothreitol affected the dodecylsulphate gel electrophoresis patterns of S. albus membranes and soluble fractions. This effect resulted from the reduction of pre-existing disulfide intramolecular bridges and some interchain disulfide formed during solubilization and/or storage. Dithiothreitol also affected the dodecylsulphate gel electrophoresis patterns of E. coli membranes and their soluble fractions. These results suggest that sulfhydryl groups and disulfide bridges play a role in the structural organization of these prokaryotic membranes.