The isolation and characterisation of the plasma membrane fromHalobacterium salinarium

The plasma membrane ofHalobacterium salinarium, strain 1, has been isolated and characterised. A fraction containing cell envelope vesicles was isolated from a cell homogenate by centrifuging. A crude membrane fraction was obtained from the envelope fraction by dialysing it against distilled water, incubating with nucleases and centrifuging. A nucleotide-free purified membrane fraction, identified with the plasma membrane, was obtained by gel-filtration chromatography of the crude membrane fraction on Agarose. The nucleotide-free membrane-rich fraction contained all the cell lipid, including menaquinone and carotenoid, and cytochrome. No amino sugars could be detected. The action of the detergent, sodium dodecyl sulphate, on the nucleotide-free membrane-rich fraction broke up the membrane into smaller particles. The disaggregation occurred in at least two distinct steps. The disaggregated particles could be reaggregated to a fraction which resembled the original membrane by removing the detergent by dialysis or gel-filtration. A fraction which may be analogous to mitochondrial structural protein was isolated by ammonium sulphate fractionation of a preparation of the nucleotide-free membrane-rich fraction dissolved in a mixture of sodium deoxycholate, sodium cholate and sodium dodecyl sulphate. Protein fractions were separated from the nucleotide-free membrane-rich fraction during gel-filtration chromatography on Agarose in the presence of 6m urea. The authors would like to acknowledge the technical assistance of Miss C. Goode and Mrs. J. Wicks. We are indebted to Mrs. A. Flo of the Department of Biochemistry, The Technical University of Norway, Trondheim, for technical assistance in the preparation of samples for electron microscopy.