Distribution of protein kinase activities in subcellular fractions of rat brain.

The subcellular distribution of histone and phosvitin kinase activities in brain has been studied and the ability of the various fractions to catalyse the phosphorylation of their endogenous proteins (intrinsic protein kinase activity) also examined. Synaptosome membrane fragments have little or no histone or phosvitin kinase activity but contain the highest concentration of cyclic AMP-stimulated intrinsic protein kinase activity. Homogenisation of the membrane fragments in Triton X-100 increased the histone kinase activity but on centrifugation it was all recovered in the supernatant, while the insoluble material contained all the intrinsic protein kinase activity. These results indicate that the intrinsic protein kinase activity of cerebral membrane fragments is due to the presence of a kinase enzyme which is specific to certain membrane proteins. The intrinsic protein kinase activity of synaptosome membrane fragments is a rather slow reaction which takes several minutes to saturate all the acceptor proteins.