Intrinsic protein phosphorylation in synaptic plasma membrane fragments from the rat. General characteristics and migration behaviour on polyacrylamide gels of the main phosphate acceptors.

Preparations enriched in synaptic membrane fragments from rat cerebral cortex contain protein kinases which phosphorylate membrane proteins in reactions dependent on cAMP, Ca2+ (in the absence of presence of calmodulin) or independent of these factors. In the present work characteristics of the main phosphorylated acceptors were studied and compared with the results of other investigations. Apparent molecular weights were estimated by determining electrophoretic mobility on gels of different acrylamide concentration. Irregular migration behaviour was detected by measuring free mobilities from Ferguson plots. Certain phosphate acceptors were found to exhibit anomalously low free mobilities and it was concluded that estimates of molecular weight for these acceptors were unreliable.