| Abstract: | As cultures of Escherichia coli progressed from the exponential growth phase to the stationary growth phase, the phospholipid composition of the cell was altered. Unsaturated fatty acids were converted to cyclopropane fatty acids, and phosphatidyl glycerol appears to have been converted to cardiolipin. With dual isotope label experiments, the kinetics of synthesis of cyclopropane fatty acid for each of the phospholipids was examined in vivo. The amount of cyclopropane fatty acid per phospholipid molecule began to increase in phosphatidyl ethanolamine at a cell density below the density at which this increase was observed in phosphatidyl glycerol or cardiolipin. The rate of this increase in phosphatidyl glycerol or in cardiolipin was faster than the rate of increase in phosphatidyl ethanolamine. After a few hours of stationary-phase growth, all the phospholipids were equally rich in cyclopropane fatty acids. It is suggested that the phospholipid alterations observed are a mechanism to protect against phospholipid degradation during stationary phase growth. Cyclopropane fatty acid synthetase activity was assayed in cultures at various stages of growth. Cultures from all growth stages examined had the same specific activity in crude extracts. |
