Partial purification of diphosphatidylglycerol synthetase from liver mitochondrial membranes.

The enzyme responsible for the conversion of phosphatidylglycerol to diphosphatidylglycerol (cardiolipin) in the presence of cytidine diphosphate diacylglycerol is firmly associated with 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 zwitter-ionic 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 phosphatidyl-glycerols, 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+ much greater than Mn2+ greater than Mg2+. In the presence of optimal levels of Co2+ other divalent cations are inhibitory with the order of inhibition: Cd2+ greater than Zn2+ greater than Ca2+ greater than Ba2+ greater than Cu2+ greater than Hg2+ greater than Ni2+. The solubilized enzyme exhibited no requirement for added phospholipids and several phospholipids inhibited the reaction in the order: diphosphatidylglycerol greater than phosphatidylethanolamine greater than phosphatidylserine greater than phosphatidylinositol.

Purification and properties of phosphatidylglycerophosphate synthetase from mammalian liver mitochondria.

The enzyme which catalyzes the synthesis of phosphatidylgly cerophosphate from an-glycerol-3-phosphated and cytidine diphosphate diacylglycerol was released from rat or pig liver mitochondrial membranes by extraction with Triton X-100 or Nonidet P-40. The detergent-extracted enzyme, like the activity of intact mitochondria, did not require added cations or lipids. The Triton extracts were fractionated by column chromatography on Bio-Gel A-1.5. The fractions obtained from the columns exhibited little activity in the standard assay system unless divalent cations were included. Additional stimulation (about twofold) was observed in the presence of added phospholipids. The cation requirement of the purified enzyme was relatively nonspecific with Mg2+, Ba2+, or Ca2+ providing maximal activity in the 10mM range. Either Mn2+ or Co2+ were stimulatory at somewhat lower concentrations but higher concentrations were inhibitory. Other cations such as Cd2+, Zn2+,Hg2+, or Cu2+ were ineffective as cofactors, and in the presence of Mg2+ inhibited the reaction at concentrations greater than 0.5 mM. The phospholipik stimulation was obtained specifically with phosphatidylethanolamines from natural or synthetic sources. Other diacylglycerophosphatides or lysophosphatides including lysophosphatidylethanolamine were ineffective.