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Volume 271, Number 40, Issue of October 4, 1996 pp. 24395-24400
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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Characterization of the Active Site Iron in Tyrosine Hydroxylase
REDOX STATES OF THE IRON

(Received for publication, May 8, 1996, and in revised form, June 7, 1996)

Andrew J. Ramsey , Patrick J. Hillas and Paul F. Fitzpatrick ^§

From the Departments of  Biochemistry and Biophysics and ^§ Chemistry, Texas A&M University, College Station, Texas 77843-2128

Tyrosine hydroxylase is an iron-containing monooxygenase that uses a tetrahydropterin to catalyze the hydroxylation of tyrosine to dihydroxyphenylalanine in catecholamine biosynthesis. The role of the iron in this enzyme is not understood. Purification of recombinant rat tyrosine hydroxylase containing 0.5-0.7 iron atoms/subunit and lacking bound catecholamine has permitted studies of the redox states of the resting enzyme and the enzyme during catalysis. As isolated, the iron is in the ferric form. Dithionite or 6-methyltetrahydropterin can reduce the iron to the ferrous form. Reduction by 6-methyltetrahydropterin consumes 0.5 nmol/nmol of enzyme-bound iron, producing quinonoid 6-methyldihydropterin as the only detectable product. In the presence of oxygen, reoxidation to ferric iron occurs. During turnover the enzyme is in the ferrous form. However, a fraction is oxidized during turnover; this can be trapped by added catechol or by the dihydroxyphenylalanine formed during turnover.

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