Rottem S, Greenberg A S
J Bacteriol. 1975 Feb;121(2):631-9. doi: 10.1128/jb.121.2.631-639.1975.
During the progression of Mycoplasma hominis cultures from the early logarithmic phase to the stationary phase of growth, the total phospholipid content of the cell membranes decreased. Measurement of the amount of the various phospholipids during the growth cycle showed that a decrease in the phosphatidylglycerol (PG) content, accompanied by an increase in the phosphatidic acid content, occurred upon aging of the culture. Pulse labeling experiments revealed that the PG, once formed, is relatively stable, undergoing no detectable turnover in growing cultures of M. hominis. No changes in the fatty acid composition of the membrane phospholipids were observed on aging of the culture, with palmitic acid predominating throughout the growth cycle. The preferential incorporation of palmitate into the phospholipid fraction is apparently caused by the higher activity of the membrane-bound acyl-coenzyme A (CoA):alpha-glycerophosphate transacylase with palmityl-CoA rather than with oleyl-CoA as substrate. The activity of the soluble acyl-CoA synthetase was the same whether palmitate or oleate served as substate. M. hominis membrane preparations contained a PG-synthetase system catalyzing the incorporation of L-alpha-glycerol-3-phosphate into PG. The activity of the PG synthetase system was markedly dependent on the age of the culture, being highest in cells from the early exponential phase of growth while declining sharply thereafter, and thus probably responsible, in part, for the decrease in PG content upon aging of the cells. Electron paramagnetic resonance spectra of a spin-labeled fatty acid incorporated in M. hominis membranes revealed a marked decrease in the freedom of motion of the spin label on aging of the culture. It is proposed that this decrease is due primarily to the decrease in the lipid-to-protein ratio of the membranes and has a marked effect on the activity of membrane-associated enzymes and transport systems.
在人型支原体培养物从生长早期对数期进入稳定期的过程中，细胞膜的总磷脂含量降低。对生长周期中各种磷脂含量的测定表明，随着培养物老化，磷脂酰甘油（PG）含量降低，同时磷脂酸含量增加。脉冲标记实验表明，一旦形成，PG相对稳定，在人型支原体生长培养物中未检测到其周转。培养物老化时，膜磷脂的脂肪酸组成未观察到变化，在整个生长周期中棕榈酸占主导。棕榈酸优先掺入磷脂部分显然是由于膜结合的酰基辅酶A（CoA）：α-甘油磷酸转酰基酶以棕榈酰CoA而非油酰CoA作为底物时活性更高。无论以棕榈酸还是油酸作为底物，可溶性酰基辅酶A合成酶的活性相同。人型支原体膜制剂含有一个PG合成酶系统，催化L-α-甘油-3-磷酸掺入PG。PG合成酶系统的活性明显依赖于培养物的年龄，在生长早期指数期的细胞中最高，此后急剧下降，因此可能部分导致细胞老化时PG含量的降低。掺入人型支原体膜中的自旋标记脂肪酸的电子顺磁共振光谱显示，随着培养物老化，自旋标记的运动自由度显著降低。有人提出，这种降低主要是由于膜的脂质与蛋白质比率降低，并且对膜相关酶和转运系统的活性有显著影响。
