The enzymatic incorporation of stn-glycerol 3-phosphate into lipid by extracts of cucumber (Cucumis sativus) cotyledons showed an absolute requirement for ATP (saturation 2 mM). The incorporation was stimulated 4-fold by 0.2 mM oleate. Ethyldiaminetetraacetate stimulated the incorporation at concentrations below 1 mM and inhibited at higher concentrations. Mg2+ did not affect the reaction. Triton X-100 and Cutscum inhibited the reaction, while a third detergent, Span 80, was stimulatory. p-Mercuribenzoate was inhibitory. The enzymatic reaction has a pH optimum in the range of 8.8 to 9.6. The Michaelis constant was 112 ,uM for sn-glycerol 3-phosphate. The major amount of product was phosphatidic acid, the remainder was diacylglycerol, monoacylglycerol, and an unknown phospholipid. We have asked the second question in response to a suggestion put forward by Pieringer et al. (24) in a paper on PA synthesis in E. coli. They have shown that E. coli can synthesize PA by two separate reactions: (a) acylation of sn-glycerol 3-phosphate, and (b) phosphorylation of 1, 2-diacyl-sn-glycerol. The first reaction accounts for de novo synthesis. Pieringer et al. (24) have suggested that the second reaction acts as a scavenger system for glycerides formed from partially degraded phospholipids. Since bacteria must rapidly conform to changing environments (for example via membrane alterations), an enzyme system capable of utilizing partially degraded phospholipids for new phospholipid synthesis would be more efficient than a system using the products from fully degraded phospholipids. In the same manner, plants could benefit by phosphorylating partially degraded triacylglycerols to provide phospholipid precursors during germination. Bradbeer and Stumpf (6) have reported the diglyceride kinase activity in peanut cotyledons. MATERIALS AND METHODS