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Methylamine dehydrogenase is a light-dependent oxidase
1Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS 39216-4505, USA.
Biochimica Et Biophysica Acta
|June 19, 1998
Summary
UV light activates tryptophan tryptophylquinone (TTQ)-linked methylamine dehydrogenase (MADH) to act as an oxidase, not a dehydrogenase. This light-induced activity is reversible and mediated by a semiquinone intermediate.
Area of Science:
- Biochemistry
- Enzymology
- Photochemistry
Background:
- Quinoproteins function as oxidases or dehydrogenases based on their quinone prosthetic group.
- Tryptophan tryptophylquinone (TTQ)-linked methylamine dehydrogenase (MADH) is typically a dehydrogenase and inert to O2 in its reduced state.
Purpose of the Study:
- To investigate the effect of UV light on MADH activity.
- To determine if light can alter the enzymatic function of MADH from a dehydrogenase to an oxidase.
Main Methods:
- Exposure of reduced MADH to long-range UV light in the presence of O2.
- Monitoring of enzymatic activity and intermediate formation.
- Reversibility studies upon removal of light.
Main Results:
- UV light induces substrate-dependent steady-state oxidase activity in MADH.
- The light-dependent oxidation involves a semiquinone intermediate accumulating to near stoichiometric levels.
- The observed oxidase activity is completely reversible upon cessation of light exposure.
Conclusions:
- Light absorption provides energy to overcome a thermodynamic barrier, enabling electron transfer from TTQ to O2.
- This study elucidates factors determining whether an oxidoreductase functions as a dehydrogenase or an oxidase.
- Photochemical activation offers a novel mechanism to switch enzyme function.