PROTOPLAST MEMBRANE OF STREPTOCOCCUS FAECALIS

Publisher Website
Google Scholar
Abstract
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.