Phospholipid requirement of acyl coenzyme A:sn-glycerol-3-phosphate acyltransferase from rat liver mitochondria.

Acyl coenzyme A:sn-glycerol-3-phosphate acyltransferase, a membrane-bound enzyme, was extracted from rat liver mitochondria in a phospholipid-depleted form. This preparation is inactive but can be reconstituted by the addition of phospholipid. Crude soybean phospholipid (asolectin) was more effective than a mixture of crude phospholipids prepared from rat liver and beef heart mitochondria. The best reconstitution was achieved with a ternary mixture of purified phospholipids consisting of phosphatidylserine, phosphatidylinositol, and phosphatidylethanolamine. Other active phospholipids, in decreasing order of effectiveness, were: asolectin, phosphatidylserine, mixtures of phosphatidylethanolamine and phosphatidylinositol, crude mitochondrial phospholipid, and phosphatidylinositol. Although phosphatidylethanolamine alone was inactive, it exhibited a synergistic effect with phosphatidylinositol and with mixtures of the latter and phosphatidylserine. Other phospholipids and surfactants were ineffective in reconstituting enzyme activity. Although palmitoyl-CoA was, in all cases, a considerably better acyl donor than oleoyl-CoA, the relative activity with oleoyl-CoA and lauroyl-CoA was significantly influenced by the polar head group of the phospholipid used to reconstitute enzyme activity. Enzyme reconstituted with phosphatidylserine was inactive with oleoyl-CoA and exhibited diminished activity with lauroyl-CoA, whereas preparations reconstituted with phosphatidylinositol or mixtures of the latter with phosphatidylethanolamine were considerably more active with both acyl donors. The combined data suggest that the phospholipid head group may be important in determining the acylCoA selectivity but not the positional specificity of the enzyme.