Enkephalins affect hippocampal membrane phosphorylation

Slices of rat brain hippocampus were incubated with methionine-enkephalin, leucine-enkephalin, [Des-Tyr 1] methionine-enkephalin or etorphin. After incubation the endogenous phosphorylation of proteins was measured using crude mitochhondrial fractions prepared from the incubated slices. Methione- and leucine-enkephalin specifically enhanced the radiophosphate incorporation into one protein band with an apparent molecular weight of 50K. The effect could also be detected in a fraction containing purified synaptosomal plasma membranes. The effect was time-and dose-dependent and could be mimicked by etorphin and blocked by naloxone. If methionineenkephalin was added directly to a membrane fraction a marked inhibition of incorporation of phosphate into the 50K band was observed. It is suggested that opiate-receptor activation underlies the effects of enkephalin on hippocampal phosphoprotein metabolism.