Diacylglycerol kinase in plasma membranes from wheat

Diacylglycerol kinase activity was demonstrated in highly purified plasma membranes isolated from shoots and roots of dark-grown wheat (Triticum aestivum L.) by aqueous polymer two-phase partitioning. The active site of the diacylglycerol kinase was localized to the inner cytoplasmic surface of the plasma membrane using isolated inside-out and right-side-out plasma membrane vesicles from roots. The enzyme activity in plasma membrane vesicles from shoots showed a broad pH optimum around pH 7. The reaction was Mg²⁺ and ATP dependent, and maximal activity was observed around 0.5 mM ATP and 3 mM MgCl₂. The Mg²⁺ requirement could be substituted only partially by Mn²⁺ and not at all by Ca²⁺. The phosphorylation of endogenous diacylglycerol was strongly inhibited by detergents indicating an extreme dependence of the lipid environment. Inositol phospholipids stimulated the activity of diacylglycerol kinase in plasma membranes from shoots and roots, whereas the activity was inhibited by R59022, a putative inhibitor of several diacylglycerol kinase isoenzymes involved in uncoupling diacylglycerol activation of mammalian protein kinase C.