Tyrosine hydroxylase, a member of the aromatic amino acid hydroxylase family, uses a mononuclear Fe(II) and tetrahydropterin for hydroxylation of tyrosine to dihydroxyphenylalanine. Rapid-freeze quench Mössbauer spectroscopy has now provided direct evidence for the presence of an Fe(IV) intermediate in the reaction catalyzed by tyrosine hydroxylase. Rapid-quench techniques provide support for the kinetic competence of this species as the hydroxylating intermediate. This is the first direct evidence for a mononuclear Fe(IV) intermediate in an enzymatic aromatic hydroxylation reaction.
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