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Molecular Pharmacology, Vol 13, 44-49, Copyright © 1977 by the American Society for Pharmacology and Experimental Therapeutics
-aminoethyl ether)-N,N'-tetraacetic
Acid and Calcium on Tyrosine Hydroxylase Activity
1 Section on Biochemical Pharmacology, Hypertension-Endocrine Branch, National Heart and Lung Institute,
Bethesda, Maryland 20014
It has been suggested that calcium plays a role in the regulation of tyrosine hydroxylase
[tyrosine 3-monooxygenase; L-tyrosine,tetrahydropteridine oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.21 activity. We have studied the effects of calcium and the
calcium-chelating agent ethylene glycol bis(
-aminoethyl ether)-N,N'-tetraacetic acid
(EGTA) on tyrosine hydroxylase activity in vitro. The enzyme was assayed with both
optimal and suboptimal concentrations of substrate and cofactor, and with both a
chemical and an enzymatic system for maintaining the cofactor in the reduced state. We
did not observe any significant stimulation by EGTA of tyrosine hydroxylase in crude
extracts prepared from rat striatum, hypothalamus, or adrenal glands. In addition,
there was no appreciable effect of calcium on tyrosine hydroxylase in crude striatal
extracts. These results do not support the hypothesis that EGTA stimulates tyrosine
hydroxylase in dopaminergic neurons.