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 phosp hatases was examined over endogenous substrates, using specific effect ors of these enzymes. cAMP-dependent protein kinase was shown to phosp horylate the 77, 60 and 51 kDa phosphoproteins and type II casein kina se, a specific 24 kDa one. On the contrary, types 1 and 2A protein pho sphatases seemed to have a broad specificity in plasma membranes. An a nalysis of the phosphoprotein pattern based on the endogenous substrat es 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.