[Biochemical and ultrastructural characteristics of the membranes of Streptococcus faecalis]

Abstract

It is demonstrated by thin-section that S. faecalis cells (Strain BKM-B6) have no inner membranes, and their plasma membranes do not show any invagination into the cytoplasm. It is established that B and A fracture faces of the membranes in the intact bacteria, protoplasts, osmotic shock and sonicated membrane fractions contain uniformly distributed particles with a density of 200--400 and 4000--5000 particles/mu m2, respectively. Washing of the osmotic shock membrane fraction with a buffer solution of 0.25 M tris-SO4 with 2 M LiCl removes 35--40% of non-membrane proteins. Further washing (repeated 3 times) of the fraction with 0.001 M tris-SO4 removes additionally 40% of the protein, decreases the ATPase activity by 80%, and slightly decreases the cross-section of the membranes, but it does not affect of their A and B fracture faces. The membrane fracture faces A in all fractions exhibit small areas with tetragonally packed particles (with a tetragon size of 150 A X 150 A and a density of 20000--22000 particles/mu m2). These areas seem to be responsible for changing in the isolated membrane properties. Treatment of the washed membrane fractions with 0.2% triton X-100 results in a decrease of the vesicle sizes and appearance of drastic changes of their fracture faces. Changes of the membrane fracture faces under the action of triton X-100 are likely to be due to a breakdown in the hydrophobic interaction between the protein and lipid components. As it is shown by freez-fracturing technique, osmotic shock and sonicated membrane fractions contain 95% and 50% of rightside-out vesicles. It correlates with biochemical data on the membrane orientation of vesicles in different fractions.