The effect of different molecular species of sphingomyelin on phospholipase C delta 1 activity.

Bovine brain sphingomyelin was separated into different molecular species using a reverse phase column. PLC delta 1 was inhibited by all molecular species of sphingomyelin. The extent of this inhibition was dependent on the hydrophobicity. Based on fatty acid analysis, we conclude that the inhibition of PLC delta 1 depends on the chain length and degree of unsaturation of the fatty acid moiety of SM. N-palmitoyl-D-sphingomyelin and N-stearoyl-D-sphingomyelin inhibited PLC delta 1 less then N-oleoyl-D-sphingomyelin. In the absence of Ca2+ (1 mM EGTA) all tested molecular species of SM inhibited weakly the enzyme. The sensitivity of PLC delta 1 to inhibition by SM increased with increasing Ca2+ concentration. The shape of calcium curve differed for molecular species with saturated and unsaturated fatty acids. Inhibition of PLC delta 1 by N-palmitoyl-D-sphingomyelin and N-stearoyl-D-sphingomyelin reached a maximum at 0.2 microM Ca2+, while inhibition by N-oleoyl-D-sphingomyelin reached maximum at 2 microM Ca2+. PLC delta 1 is more sensitive to inhibition by SM when it is maximally activated by spermine and calcium and the extent of this inhibition depends on the length and degree of fatty acid unsaturation of the molecular species.