Abstract
Aldehyde oxidase (AO) is a homodimer with a molecular weight of 300 kDa. To clarify the reasons for the well-known differences in rat strains, we set out to study the relationship between AO activity and the expression levels of its dimer. AO-catalyzed 2-oxidation activity of (S)-RS-8359 was measured in liver cytosols from ten rat strains. The expression levels of AO dimeric protein were evaluated by the native-PAGE/Western blot. Rat strains with low AO activity showed only a monomer, whereas strains with high activity overwhelmingly exhibited a dimer. Exceptionally, one strain in the high AO activity group displayed complex mixed expression patterns of low and high AO activity groups. However, there was a good relationship between AO activity and the expression levels of a dimer, but not of a monomer. The results suggest that rat strains with low AO activity lack the ability to produce a dimer necessary for catalytic activity, and AO differences in rat strains should be discussed in terms of the expression levels of the dimer itself.
Acknowledgements
We thank to Dr T. Ikeda, Director of the Drug Metabolism and Pharmacokinetics Research Laboratories, Sankyo Co. Ltd, and Drs K. Nishimura and Y. Kawahara, Ex-directors of the Research Laboratories, for their kind encouragement.