Specificity of rat liver plasma membrane serine/threonine protein kinases and phosphatases over endogenous proteins.

The specificity of rat liver plasma membrane protein kinases and phosphatases was examined over endogenous substrates, using specific effectors of these enzymes. cAMP-dependent protein kinase was shown to phosphorylate the 77, 60 and 51 kDa phosphoproteins and type II casein kinase, a specific 24 kDa one. On the contrary, types 1 and 2A protein phosphatases seemed to have a broad specificity in plasma membranes. An analysis of the phosphoprotein pattern based on the endogenous substrates of plasma membrane enzymes was deduced from these and other results from our laboratory. The specificity of some enzymes might arise from the anchorage in plasma membrane which might restrict their activity to their immediate environment.