Modulation of phospholipase A2 activity by neutral and anionic glycosphingolipids in monolayers.

The effect of neutral (galactocerebroside and asialo-ganglioside GM1) or anionic (sulphatide and gangliosides GM1, GD1a and GT1b) glycosphingolipids on the activity of phospholipase A2 from pig pancreas was studied in mixed monolayers of dilauroyl phosphatidylcholine with the glycosphingolipids in different molar fractions at various constant surface pressures. The activity of the enzyme depends on the proportion and type of glycosphingolipid in the interface. Sulphatide activates the enzyme at all proportions, whereas galactocerebroside shows inhibition or activation depending on its proportion in the film. Asialo-ganglioside GM1 and gangliosides GM1, GD1a and GT1b can strongly inhibit the enzyme at relatively low molar fractions in the film in the following order: asialo-ganglioside GM1 less than ganglioside GM1 less than ganglioside GT1b less than ganglioside GD1a. The changes of activity are not due to a direct action of the lipids on the active centre or interfacial recognition region of the enzyme.