INHIBITION BY GANGLIOSIDES OF BACILLUS-CEREUS PHOSPHOLIPASE-C ACTIVITY AGAINST MONOLAYERS, MICELLES AND BILAYER VESICLES

The effect of complex glycosphingolipids (gangliosides) on the activit y of phospholipase C from Bacillus cereus was studied using lipid mono layers, mixed micelles and small unilamellar vesicles containing phosp hatidylcholine as substrate. In all artificial membrane systems assaye d, gangliosides exhibit qualitatively similar inhibitory properties. G angliosides decrease the enzyme activity irrespective of the aggregati on structure in which the substrate is offered to B. cereus phospholip ase C, and they do not affect the adsorption process of the enzyme. Th e modulatory effect of gangliosides occurs at the level of the interfa ce, affecting both the maximum rate of catalysis of the enzyme already adsorbed and the availability of the substrate in a suitable organiza tion for enzyme catalysis to take place.