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

Abstract

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.