Partial purification of diphosphatidylglycerol synthetase from liver mitochondrial membranes

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Abstract
The enzyme responsible for the conversion of phosphatidylglycerol to diphosphatidylglycerol (cardiolipin) in the presence of cytidine diphosphate diacylglycerol is firmly associated with [rat or pig liver] mitochondrial membranes and is not extracted with hypotonic or hypertonic media or with nonionic detergents. Some solubilization was obtained with bile salt solutions, but the zwitterionic detergent, Miranol H2M, was most effective in extracting the enzyme. The Miranol extracts were fractionated by column chromatography on Bio-Gel A-1.5 m. The solubilized enzyme is considerably more active in converting unsaturated than saturated phosphatidylglycerols, but shows little preference for the cytidine diphosphate diacylglycerols with different fatty acyl substituents. There is an absolute dependence upon divalent cations with the order of effectiveness: Co2+ .mchgt. Mn2+ > Mg2+. In the presence of optimal levels of Co2+ other divalent cations are inhibitory with the order of inhibition: Cd2+ > Zn2+ > Ca2+ > Ba2+ > Cu2+ > Hg2+ > Ni2+. The solubilized enzyme exhibited no requirement for added phospholipids and several phospholipids inhibited the reaction in the order: diphosphatidylglycerol > phosphatidylethanolamine > phosphatidylserine > phosphatidylinositol.

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