The effect of different molecular species of sphingomyelin on phospholipase C δ1 activity

Abstract Bovine brain sphingomyelin was separated into different molecular species using a reverse phase column. PLC δ1 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 δ1 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 δ1 less then N-oleoyl-D-sphingomyelin. In the absence of Ca 2+ (1 mM EGTA) all tested molecular species of SM inhibited weakly the enzyme. The sensitivity of PLC δ1 to inhibition by SM increased with increasing Ca 2+ concentration. The shape of calcium curve differed for molecular species with saturated and unsaturated fatty acids. Inhibition of PLC δ1 by N-palmitoyl-D-sphingomyclin and N-stearoyl-D-sphingomyclin reached a maximum at 0.2 μM Ca 2+ , while inhibition by N-oleoyl-D-sphingomyclin reached maximum at 2 μM Ca 2+ . PLC δ1 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.