Lipid Phosphorylation in Chloroplast Envelopes

Lipid phosphorylation takes place within the chloroplast envelope. In addition to phosphatidic acid, phosphatidylinositol phosphate, and their corresponding lyso-derivatives, we found that two novel lipids underwent phosphorylation in envelopes, particularly in the presence of carrier-free [gamma-(32)P]ATP. These two lipids incorporated radioactive phosphate in chloroplasts in the presence of [gamma-(32)P]ATP or [(32)P]P(i) and light. Interestingly, these two lipids were preferentially phosphorylated in envelope membranes in the presence [gamma-(32)P]CTP, as the phosphoryl donor, or [gamma-(32)P]ATP, when supplemented with CDP and nucleoside diphosphate kinase II. The lipid kinase activity involved in this reaction was specifically inhibited in the presence of cytosine 5'-O-(thiotriphosphate) (CTPgammaS) and sensitive to CTP chase, thereby showing that both lipids are phosphorylated by an envelope CTP-dependent lipid kinase. The lipids were identified as phosphorylated galactolipids by using an acid hydrolysis procedure that generated galactose 6-phosphate. CTPgammaS did not affect the import of the small ribulose-bisphosphate carboxylase/oxygenase subunit into chloroplasts, the possible physiological role of this novel CTP-dependent galactolipid kinase activity in the chloroplast envelope is discussed.