The effect of sn-2 fatty acid substitution on phospholipase C enzyme activities.
The human monocyte cell line U937 expresses phospholipase A2 and phospholipase C activities and produces eicosanoids. The phospholipase C (PLC) activity exhibits substrate preference for phosphatidyl-choline (PC), rather than phosphatidylinositol or phosphatidylethanolamine. In order to characterize the PLC activity found in these cells, the effects of substitution of the sn-2 fatty acid on this activity were examined. PC substrates with palmitic acid (PC-2P), oleic acid (PC-2O), arachidonic acid (PC-2A) and linoleic acid (PC-2L) at the sn-2 position were used. The sn-1 fatty acid was palmitic acid. PC-2L and PC-2A with the longer-chain less-saturated fatty acids linoleic acid and arachidonic acid esterified at sn-2 were found to be better substrates for PLC activity than PC-2P or PC-2O in these cells. This preference was maintained even when substrate phospholipid was solubilized in non-ionic, anionic, cationic and zwitterionic amphiphiles. Furthermore, when a 500-fold excess of 1,2-diolein or 1,2-dipalmitin was added to the reaction, the specificity of the PLC activity for PC-2A and PC-2L remained unchanged. When similar experiments were performed with phosphatidylinositol as a substrate, we did not observe any effect when the sn-2 position was altered. These data show that the fatty acid constituent at the sn-2 position affects the observed PLC activity when phosphatidylcholine, but not phosphatidylinositol, is used as a substrate by these cells.
Bomalaski
J S
JS
Department of Medicine, Philadelphia Veterans Administration Medical Center, PA 19104.
Clark
M A
MA
D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D003902:Detergents / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008823:Micelles; D011506:Proteins / Q000494:pharmacology; D013329:Structure-Activity Relationship; D010738:Type C Phospholipases / Q000378:metabolism*
D003902:Detergents; D004075:Diglycerides; D005227:Fatty Acids; D008823:Micelles; D011506:Proteins; D010738:Type C Phospholipases; D002118:Calcium