Inhibition of Cardiolipin Synthesis by End-Products and Other Complex Lipids in Membrane Preparations of Micrococcus lysodeikticus

Using membrane preparations of Micrococcus lysodeikticus, the end-products of cardiolipin synthesis, cardiolipin and glycerol, were shown to inhibit cardiolipin synthetase at several concentrations. Other phospholipids tested for inhibitory effects, phosphatidylethanolamine, phosphatidylinositol, and phosphatide acid were also shown to inhibit cardiolipin synthesis. Phosphatidic acid was considerably more inhibitory than cardiolipin, phosphatidylethanolamine was similar to cardiolipin, and phosphatidylinositol less inhibitory at the same concentrations. A non-phosphate-containing glycolipid was also inhibitory. In contrast, glycerophosphate had no effect on cardiolipin synthesis.

THE INCORPORATION OF α-GLYCEROPHOSPHATE-32P INTO THE LIPIDS OF RAT BRAIN PREPARATIONS: II. ON THE BIOSYNTHESIS OF MONOPHOSPHOINOSITIDE

Previous investigations conducted in this laboratory showed a number of differences in the cytosine nucleotide requirement for the incorporation of α-glycerophosphate (α-G32P) into the monophosphoinositide of rat brain preparations compared to the pathway described by Paulus and Kennedy, where α-glycerophosphate → phosphatide acid → CDP-diglyceride → monophosphoinositide, and CTP is specifically required. Experiments were carried out with rat brain preparations to determine the nature of the mechanism whereby CDP-choline is as effective as or more effective than CTP in stimulating the incorporation of α-G32P into monophosphoinositide. Isotope dilution experiments in which unlabeled phosphatidic acid and CDP-diglyceride were used, yielded results consistent with the view that both of these compounds are intermediates in the incorporation of a-G32P into monophosphoinositide stimulated by either CTP or CDP-choline. Time-course experiments where cytosine nucleotides were added either at the beginning or after 20 minutes produced a pattern of labeling which could be fitted into the above interpretation, provided that newly formed radioactive molecules of phosphatide acid could be used selectively and CTP in some way inhibits phosphatide acid formation or accumulation. The latter could account for the observation that monophosphoinositide becomes far more actively labeled than phosphatidic acid in the presence of added CTP.

BIOSYNTHESIS OF LIPIDS IN PLANTS: II. INCORPORATION OF GLYCEROPHOSPHATE-32P INTO PHOSPHATIDES BY CELL-FREE PREPARATIONS FROM SPINACH LEAVES

Cell-free homogenates of spinach leaves incorporated glycerophosphate-32P into phosphatides when supplied with adenosine triphosphate, Mg++and coenzyme A (CoA). Most of the activity of the homogenate was associated with the microsome fraction sedimented at 104,000 × g, but some activity was also present in the chloroplast fraction. In all systems, most of the32P incorporated appeared in phosphatide acid (+ lysophosphatidic acid), with small to trace amounts in phosphatidyl glycerol and phosphatidyl inositol. Coenzyme A and adenosine triphosphate + Mg++were obligatory cofactors for the incorporation of α-glycerophosphate-32P but acetate + bicarbonate, cytidine triphosphate, or light were not essential. The results demonstrate the presence of acyl-CoA:L-glycerol-3-phosphate O-acyltransferase in the microsome fraction of spinach leaves and also indicate the existence of enzyme systems catalyzing the conversion of phosphatidic acid to phosphatidyl inositol and phosphatidyl glycerol.