HETEROTETRAMERS OF HUMAN LIVER MITOCHONDRIAL (CLASS 2) ALDEHYDE DEHYDROGENASE EXPRESSED IN ESCHERICHIA-COLI - A MODEL TO STUDY THE HETEROTETRAMERS EXPECTED TO BE FOUND IN ORIENTAL PEOPLE

About 50% of the Oriental population have less liver mitochondrial ald ehyde dehydrogenase (ALDH2) activity than do other people. It was foun d that they possessed an enzyme with a lysine at position 487 (E487K) instead of glutamate (GlU(487)). We previously found that the K-m, for NAD of recombinant human and rat E487K enzymes increased more than 15 0-fold (Farres, J., Wang X., Takahashi, IC, Cunningham, S. J., Wang, T .T., and Weiner, H (1994) J, Biol. Chem 269, 13854-13860). Many aldehy de dehydrogenase-deficient people were found to be heterozygous when g enotyped for ALDH2, In this study liver tissue from heterozygous peopl e was analyzed and found to possess mRNAs for both the glutamate and t he lysine subunits, Western blot analysis showed that the glutamate su bunit was present, The cDNAs for Glu(487) and E487K were coexpressed o n one plasmid in Escherichia coli, and the enzyme forms were separated from each other by isoelectric focusing to show that heterotetramers were formed. Only one LC, value for NAD could be measured with the pur ified heterotetrameric enzyme that possessed just 16-18% activity of t he glutamate homotetrameric enzyme, The E487K homotetramers had 8% spe cific activity of the GlU(487) enzyme, There was no pre-steady state b urst of NADH formation with the heterotetramer, a property found with the glutamate enzyme, Similar results were found for the coexpressed r at liver enzyme, except that a higher specific activity, 48%, was obta ined, Thus, we conclude that presence of the lysine subunit altered th e activity of the glutamate subunit in the heterotetramer to make it f unction more like an E487K enzyme.