Mechanism of phosphatidylinostiol stimulation of lysosomal bis (monoacylglyceryl)phosphate synthesis.

A soluble enzyme preparation obtained from rat liver lysosomes catalyzed the conversion of phosphatidyl-[1',3'-14C]glyceryol to [14C]bis(monoacylglyceryl)phosphate. When this preparation was delipidated with n-butyl alcohol, very low activity was observed when incubated with phosphatidyl[1',3'-14C]glycerol alone. The activity could be restored by incubating with aqueous dispersions of lysosomal phospholipids; lysosomal neutral lipid and glycolipid fractions were inactive. When the pospholipid fraction was separated into individual classes, activity was found only in phosphatidylinositol. With a more extensively delipidated soluble enzyme preparation from lysosomes, bis-(monoacylglyceryl)P synthesis without added lipid was 0.05 nmol mg-1 h-1 versus 5.9 nmol-1 h-1 at the optimal phosphatidylinositol concentation. The mechanism of this marked stimulation of bis(monoacylglyceryl)P synthesis by phosphatidylinostiol was examined. Evidence is presented which demonstrates the incorporation of 3H-labeled fatty acids from [3H]phosphatidylinositol into bis(monoacylglyceryl)P. Phosphatidylinositol stimulates the reaction by serving as an acyl donor to phosphatidylglycerol or lysophosphatidylglycerol, the substrates for bis(monoacylglyceryl)Psynthesis.