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Calcium, ATP, and Magnesium Activate Soluble Tyrosine Hydroxylase from Rat Striatum
Author(s) -
Iuvone P. Michael
Publication year - 1984
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1984.tb05395.x
Subject(s) - chemistry , tyrosine hydroxylase , leupeptin , tyrosine 3 monooxygenase , biochemistry , protein kinase a , calcium , enzyme activator , pteridine , protease , enzyme , biophysics , biology , organic chemistry
Soluble tyrosine hydroxylase (TH) prepared from rat striatum by sonication, centrifugation, and gel filtration on Sephadex G‐25 was activated by preincubation with Ca 2+ , ATP, and Mg 2+ . Activation occurred with micromolar concentrations of Ca 2+ and required the presence of both ATP and Mg 2+ . The activation was reversible and was characterized by a large decrease of apparent K m for the pteridine cofactor and a small increase of V max ‐Ca 2+ ‐induced activation was small when TH activity was assayed at pH values near the optimum, but the magnitude of the activation increased with increasing assay pH. The activation apparently did not involve Ca 2+ ‐activated protease because it was not affected by the protease inhibitor leupeptin. Nor did it involve cyclic AMP‐dependent protein kinase, as evidenced by the failure of the heat‐stable inhibitor of this kinase to decrease Ca 2+ ‐induced TH activation. Furthermore, the activation of TH evoked by Ca 2+ and that produced by cyclic AMP was additive. These experiments indicate that striatal TH can be activated in vitro by an endogenous Ca 2+ ‐dependent mechanism. The similarity of the Ca 2+ ‐induced activation of TH to that elicited by increased neuronal activity and terminal depolarization is discussed.