Biochemical characterization and regulation of cardiolipin synthase in Saccharomyces cerevisiae

Abstract

Cardiolipin (CL) synthase activity was characterized in mitochondrial extracts of the yeast Saccharomyces cerevisiae and was shown for the first time to utilize CDP-diacylglycerol as a substrate. CL synthase exhibited a pH optimum of 9.0. Maximal activity was obtained in the presence of 20 mM magnesium with a Triton X-100:phospholipid ratio of 1:1. The apparent Km values for phosphatidylglycerol and CDP-diacylglycerol were 1 mM and 36 μM, respectively. CL synthase activity was maximal at 45° C and heat inactivation studies showed that the enzyme retained greater than 75% of its activity at temperatures up to 55° C. To study the regulation of CL synthase, the enzyme was assayed in cells grown under conditions known to affect general phospholipid synthesis. Unlike many phospholipid biosynthetic enzymes including PGP synthase, which catalyzes the initial step in CL biosynthesis, CL synthase was not repressed in cells grown in the presence of the phospholipid precursor inositol. Detailed procedures for the enzymatic synthesis of 32P-labelled substrates are described.