THE EFFECT OF DIFFERENT MOLECULAR-SPECIES OF SPHINGOMYELIN ON PHOSPHOLIPASE-C DELTA-1 ACTIVITY

Bovine brain sphingomyelin was separated into different molecular spec ies using a reverse phase column. PLC delta 1 was inhibited by all mol ecular species of sphingomyelin. The extent of this inhibition was dep endent on the hydrophobicity. Based on fatty acid analysis, we conclud e that the inhibition of PLC delta 1 depends on the chain length and d egree of unsaturation of the fatty acid moiety of SM. N-palmitoyl-D-sp hinomyelin and N-stearoyl-D-sphingomyelin inhibited PLC delta 1 less t hen N-oleoyl-D-sphingomyelin. In the absence of Ca2+ (1 mM EGTA) all t ested molecular species of SM inhibited weakly the enzyme. The sensiti vity of PLC delta 1 to inhibition by SM increased with increasing Ca2 concentration. The shape of calcium curve differed for molecular spec ies with saturated and unsaturated fatty acids. Inhibition of PLC delt a 1 by N-palmitoyl-D-sphingomyelin and N-stearoyl-D-sphingomyelin reac hed a maximum at 0.2 mu M Ca2+, while inhibition by N-oleoyl-D-sphingo myelin reached maximum at 2 mu M Ca2+. PLC delta 1 is more sensitive t o inhibition by SM when it is maximally activated by spermine and calc ium and the extent of this inhibition depends on the length and degree of fatty acid unsaturation of the molecular species.