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Functional analysis of aldehyde oxidase using expressed chimeric enzyme between monkey and rat
Kunio Itoh1, Tasuku Asakawa, Kouichi Hoshino
1Department of Drug Metabolism and Pharmacokinetics, Tohoku Pharmaceutical University, Sendai, Japan.
Biological & Pharmaceutical Bulletin
|January 6, 2009
Summary
Investigating aldehyde oxidase (AO) domains revealed that the molybdenum cofactor (MoCo) domain influences substrate inhibition and kinetic profiles, while the 2Fe-2S/FAD domains impact electron transfer efficiency.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Aldehyde oxidase (AO) is a crucial homodimeric enzyme involved in xenobiotic metabolism.
- Each AO subunit comprises 2Fe-2S cluster, flavin adenine dinucleotide (FAD), and molybdenum cofactor (MoCo) domains, each with distinct functions.
- Understanding domain-specific contributions is vital for elucidating AO's catalytic mechanisms and substrate interactions.
Purpose of the Study:
- To investigate the functional roles of individual AO domains, particularly the MoCo domain, in substrate oxidation.
- To compare the catalytic properties and kinetic profiles of monkey and rat AO, and their chimeric variants.
- To determine how domain exchange affects substrate inhibition and electron transfer efficiency in AO.
Main Methods:
- Construction of chimeric cDNAs by exchanging 2Fe-2S/FAD and MoCo domains between monkey and rat AO.
- Expression of wild-type and chimeric AO enzymes in Escherichia coli.
- Measurement of AO-catalyzed 2-oxidation of (S)-RS-8359 and analysis of kinetic parameters (Vmax, substrate inhibition, Eadie-Hofstee profiles).
Main Results:
- Substrate inhibition in (S)-RS-8359 oxidation was observed in rat AO and monkey/rat chimeric AO, linked to the rat MoCo domain.
- A biphasic Eadie-Hofstee profile was seen in monkey AO and rat/monkey chimeric AO, associated with the monkey MoCo domain.
- Monkey AO exhibited higher Vmax values than chimeric rat/monkey AO, and chimeric monkey/rat AO showed higher Vmax than rat AO, indicating a more efficient electron transfer system in monkey AO.
Conclusions:
- The MoCo domain dictates substrate inhibition patterns and kinetic profiles (Eadie-Hofstee) of AO-catalyzed oxidation.
- The 2Fe-2S/FAD domains are critical for the overall velocity and electron transfer efficiency of the AO enzyme.
- Chimeric AO studies effectively delineate the distinct functional contributions of the MoCo and 2Fe-2S/FAD domains in aldehyde oxidase activity.
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