Molecular Organization in Bacterial Cell Membranes. Sulthydryl Groups and Disulfide Bridges in Streptomyces albus and Escherichia coli K 12 Cytoplasmic Membranes

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Abstract
Plasma membranes from S. albus had 5.2 mol of sulfhydryl groups and 6 mol of disulfide bridges/50 kg protein; E. 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 2 bacteria. Other sulfhydryl group reagents, such as N-ethylmaleimide, iodoacetamide and iodoacetic acid, were less effective. Dithiothreitol affected the dodecyl sulfate 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 dodecyl sulfate gel electrophoresis patterns of E. coli membranes and their soluble fractions. Sulfhydryl groups and disulfide bridges apparently play a role in the structural organization of these prokaryotic membranes.

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