Oxygen dependence of tyrosine hydroxylase.
Amino Acids
; 34(3): 455-64, 2008 Apr.
Article
de En
| MEDLINE
| ID: mdl-17520326
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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Collection:
01-internacional
Base de données:
MEDLINE
Sujet principal:
Oxygène
/
Tyrosine 3-monooxygenase
Limites:
Animals
/
Humans
Langue:
En
Journal:
Amino Acids
Sujet du journal:
BIOQUIMICA
Année:
2008
Type de document:
Article
Pays d'affiliation:
Norvège