Identification of protein phosphatase 2A as the major tyrosine hydroxylase phosphatase in adrenal medulla and corpus striatum: evidence from the effects of okadaic acid |
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Authors: | J Haavik D L Schelling D G Campbell K K Andersson T Flatmark P Cohen |
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Affiliation: | Department of Biochemistry, University of Bergen, Norway. |
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Abstract: | (i) The major sites on bovine adrenal tyrosine hydroxylase (TH) phosphorylated by calmodulin-dependent multiprotein kinase (CaM-MPK) and cyclic AMP-dependent protein kinase were shown to be Ser-19 and Ser-40, respectively, while Ser-40 was also phosphorylated slowly by CaM-MPK. (ii) Type 2A and type 2C phosphatases accounted for approximately 90% and approximately 10% of TH phosphatase activity, respectively, in extracts of adrenal medulla and corpus striatum assayed at near physiological free Mg2+ (1 mM), while type 1 and type 2B phosphatases had negligible activity towards TH. (iii) Incubation of adrenal chromaffin cells with okadaic acid increased TH phosphorylation by 206% and activity by 77%, establishing that type 2A phosphatases play a major role in regulating TH in vivo. |
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