Oxygen dependence of tyrosine hydroxylase.

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Rostrup M, Fossbakk A, Hauge A, Kleppe R, Gnaiger E, Haavik J

Oxygen dependence of tyrosine hydroxylase.

Amino Acids. 2008 Apr;34(3):455-64. Epub 2007 May 23.

PubMed ID

17520326 [ View in PubMed

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Abstract

The effects of dioxygen on tyrosine hydroxylase (TH) activity was studied, measuring the formation of DOPA from tyrosine, (3)H(2)O from 3,5-(3)H-tyrosine, or by direct oxygraphic determination of oxygen consumption. A high enzyme activity was observed during the initial 1-2 min of the reactions, followed by a decline in activity, possibly related to a turnover dependent substoichiometrical oxidation of enzyme bound Fe(II) to the inactive Fe(III) state. During the initial reaction phase, apparent K (m)-values of 29-45 microM for dioxygen were determined for all human TH isoforms, i.e. 2-40 times higher than previously reported for TH isolated from animal tissues. After 8 min incubation, the K (m) (O(2))-values had declined to an average of 20 +/- 4 microM. Thus, TH activity may be severely limited by oxygen availability even at moderate hypoxic conditions, and the enzyme is rapidly and turnover dependent inactivated at the experimental conditions commonly employed to measure in vitro activities.

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Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Tyrosine	Tyrosine 3-monooxygenase	Protein	Humans	Unknown	Binder	Details