Dioctanoylglycerol and phorbol diesters enhance phosphorylation of phosphoprotein B-50 in native synaptic plasma membranes.

The short chain diacylglycerol, 1,2-dioctanoylglycerol, at concentrations of 100-300 microM stimulated phosphorylation of the nervous system-specific membrane protein B-50 (Mr 48 kDa, IEP 4.5) in isolated synaptic plasma membranes both in the presence and absence of exogenous protein kinase C. Comparable enhancement of histone phosphorylation by purified protein kinase C was achieved with 1 microM neutral lipid. Phorbol dibutyrate was 100 times more potent than the diacylglycerol in stimulating endogenous B-50 kinase in the membranes, whereas 4-alpha-phorbol was without effect. These results further confirm that B-50 is phosphorylated physiologically by a C kinase. Our data are consistent with a negative feedback mechanism in which generation of 1,2-diacylglycerol by enhanced phosphatidylinositol-4,5-bisphosphate hydrolysis could stimulate B-50 phosphorylation, thereby diminishing phosphatidylinositol-4-phosphate kinase activity and decreasing phosphatidylinositol-4,5-bisphosphate biosynthesis.