Effect of proteolysis on the state of lipid phase in rat brain synaptosomal membranes

Enzymatic proteolysis of the proteins of synaptic membranes has been found to be accompanied by the promotion of lipid peroxidation probably mediated by the liberation of membrane-bound iron. As fluorescent probes pyrene and diphenylhexatriene show, the microviscosity and micropolarity of membrane lipid phase rise as a result of lipid peroxidation. Different structural changes induced by proteolysis are displayed under inhibition of lipid peroxidation. Thus, the microviscosity of the bulk lipid phase appears to be lowered and the annular lipid microviscosity raised. Another explanation of the fluorescent data for annular lipids is the exclusion of pyrene molecules from this lipid pool, leading to a reduction of the probe local concentration. The changes observed in membrane lipid phase are considered as primary structural effects of proteolysis, not mediated by a phospholipase activation.