Hydrolysis of Phosphatidylinositol by Human Pancreatic Phospholipase A2

Pure human pancreatic phospholipase A2 efficiently hydrolyzed the 2-ester bond of 14C-2-linoleoyl and 14C-2-arachidonyl phosphatidylinositol (PI). The rate of hydrolysis varied markedly with the bile salt (sodium taurocholate to sodium taurodeoxycholate, 3:4 mol/mol) concentration, the hydrolysis being decreased with increasing bile salt to PI ratio. The influence of bile salts was thus similar to that which has earlier been described for the hydrolysis of phosphatidylcholine (PC) with pig pancreatic phospholipase A2. When 2-3H-arachidonyl PC and 2-14C-arachidonyl PI were incorporated into a mixed substrate, PI was hydrolyzed even faster than PC, the hydrolysis of both phospholipids varying in the same manner with bile salt concentration. 2-14C-arachidonyl PI was also efficiently hydrolyzed by human duodenal content, although at a somewhat slower rate than 2-3H-arachidonyl PC. It is concluded that PI is a good substrate for human phospholipase A2. This minor but arachidonate-rich dietary phospholipid may thus be digested and absorbed by pathways similar to those of the major dietary and bile phospholipid, phosphatidylcholine.