Cardiolipin synthase from mammalian mitochondria.

Cardiolipin was first isolated from beef heart and was shown to contain an unusually high content of linoleic acid ester residues. Cardiolipin is found throughout the eukaryotes including animals, plants and fungi. In mammalian tissue and in yeast, cardiolipin is found exclusively in mitochondria. Mitochondrial synthesis of cardiolipin utilizes phosphatidylglycerol and CDP-diacylglycerol as substrates in a reaction which requires a divalent cation (Mg2+, Mn2+ or Co2+). Cardiolipin synthase has been purified to near-homogeneity from rat liver by solubilization with Zwittergent 3-14 followed by FPLC anion exchange, gel permeation and chromatofocusing steps. Cardiolipin synthase has a molecular mass of 50 kDa, a pH optimum of 8.0, and requires added phospholipids (phosphatidylethanolamine and cardiolipin) and 4 mM Co2+ for optimal activity. Except for the effects of divalent cations and the requirement for phospholipids, little is known about the regulation of cardiolipin synthase. Cardiolipin deficiency in aging mitochondria has been linked to decreased metabolite transport across the inner membrane. Both cardiolipin levels and cardiolipin synthase activity are increased in hyperthyroidism and decreased in hypothyroidism suggesting regulation by thyroid hormone. Mammalian cardiolipin synthase has not been sequenced or cloned and its biological role in mitochondria is not yet fully understood.