DIACYLGLYCEROL KINASE IS STIMULATED BY ARACHIDONIC-ACID IN NEURAL MEMBRANES

The effect of arachidonic acid (AA) on the activity of diacylglycerol (DG) kinase in neural membranes was investigated. When rat brain corti cal membranes were incubated with 0.5 mM dipalmitin and [gamma-P-32]AT P, formation of phosphatidic acid (PA) was observed. It was linear up to 5 min, and the initial rate was similar to 1.0 nmol/min/mg of prote in. The DG kinase activity was stimulated twofold by 0.25 mM AA. The s timulation was apparent at the earliest time point measured (1 min) an d with the lowest concentration of AA tested (62.5 mu M). The stimulat ion was proportional to the concentration of AA up to 250 mu M. AA was the most potent stimulator of DG kinase, and linolenic acid showed si milar to 40% stimulation. Oleic acid showed no effect, whereas linolei c and the saturated fatty acids tested were inhibitory. AA stimulation of DG kinase was observed only with membranes of cerebrum, cerebellum , and myelin and not with brain cytosol or liver membranes. AA also st imulated the formation of PA in the absence of added dipalmitin (endog enous activity) with membranes prepared from whole brain. DG kinase of neural membranes was extracted with 2 M NaCl, which on dialysis yield ed a precipitate. Both the precipitate and the supernatant showed DG k inase activity, but only the enzyme in the precipitate was stimulated by AA at concentrations as low as 25 mu M. It is suggested that AA, th rough its effect on DG kinase, regulates the level of DG in neural mem branes, which in turn regulates protein kinase C activity.