BIOSYNTHESIS OF CARDIOLIPIN IN PLANT-MITOCHONDRIA

The properties of cardiolipin synthase were investigated in mitochondr ia and submitochondrial fractions from etiolated mung bean (Vigna radi ate L.) seedlings. Direct evidence is presented that the enzyme utiliz es CDP-diacylglycerol in addition to phosphatidylglycerol for the synt hesis of cardiolipin. Cardiolipin synthase had an alkaline pH optimum of about 9 and required divalent cations for activity. Maximal activit y was obtained in the presence of 16 mM MnCl2. The apparent K-m values for CDP-diacylglycerol and phosphatidylglycerol were 0.8 and 50 mu M, respectively. Cardiolipin synthase was localized predominantly in the inner membrane of mung bean mitochondria and displayed a substrate sp ecies specificity. Highest activities were measured with the dioleoyl species of both CDP-diacylglycerol and phosphatidylglycerol, and somew hat tower activities were measured with mixed species of the two subst rates containing a palmitoyl and an oleoyl group. On the other hand, t he cardiolipin synthase hardly used the dipalmitoyl species and strong ly discriminated against CDP-dipalmitoyl-glycerol from a mixture with CDP-dioleoylglycerol.