Partial purification and characterization of protein phosphatases from bovine adrenal medulla

Control of neurosecretion and synthesis of neurotransmitters appears to be regulated through second messengers that change the phosphorylation state of critical enzymes and proteins. Relatively little is known about the role of protein kinases in these processes in neuronal cells and even less is known about the role of protein phosphatases. We have examined the phosphatase activities of the bovine adrenal medulla using chromatographic separation, substrate specificity and inhibitor sensitivity. When fractionated, using an HPLC ion exchange DEAE column, four distinct peaks (peaks I,II,III and IV) of phosphatase activity mere observed in the supernatant of homogenized bovine adrenal medulla. These phosphatases have distinctly different specific activities toward different substrates. Peak IV which contains most of the activity toward phosphocasein, showed preferential dephosphorylation of the alpha subunit of phosphorylase kinase relative to the beta subunit and was strongly inhibited by okadaic acid, attributes of the type 2A phosphatase. The apparent molecular weight of phosphatase peak IV is also comparable to the heterotrimeric form of the known protein phosphatase type 2A of mammalian cells.