PROTOPLAST MEMBRANE OF STREPTOCOCCUS FAECALIS

Abstract

Shockman, Gerald D. (Temple University School of Medicine, Philadelphia, Pa.), Joseph J. Kolb, Bohdan Bakay, Margaret J. Conover, and Gerrit Toennies . Protoplast membrane of Streptococcus faecalis . J. Bacteriol. 85: 168–176. 1963.—The membrane fraction of Streptococcus faecalis (ATCC 9790) was isolated and purified, by a variety of procedures, from cultures that were grown under closely controlled conditions of physiological age and nutrition. The most satisfactory method required the use of lysozyme-to-cell ratios below 0.01 and the intermediate formation of protoplasts in osmotically protective media. Amino acid analyses of three of the membrane preparations indicated a characteristic and constant, but not unusual, pattern; 42% of the membranes from threonine-depleted and 49 to 55% of the membranes from log-phase cultures were accounted for as protein. Significant quantities of d -alanine or d -aspartic acid were not detected, indicating the absence of contaminating cell-wall substance. Essentially, all of the nitrogen was accounted for as amino acids. The lipid content of membranes from stationary-phase threonine-depleted (36%) and valine-depleted (40%) cultures was significantly higher than the corresponding fraction of exponential-phase cultures (28%). The phosphorus content of the membrane lipid was relatively constant (2.8 to 3.0%), and the nitrogen content was extremely low (0.12 to 0.26%). Thus, changes in the composition of the membrane fraction occurred during the transition of log-phase cells into threonine- or valine-depleted cells.