Atypical human liver alcohol dehydrogenase: the β2-Bern subunit has an amino acid exchange that is identical to the one in the β2-Oriental chain

The ‘atypical’ human liver alcohol dehydrogenase dimer, homogeneous for β 2-Bern chains, was isolated from human liver of Caucasian individuals. It is derived from an allelic variant at the ADH 2 gene locus and exhibits a considerably higher specific activity and lower pH optimum than its ‘typical’ counterpart (isoenzyme β 1 β 1) from the β 1-chain predominant in Caucasians. Peptides were prepared by trypsin or CNBr cleavage, and were purified by exclusion chromatography and reverse-phase high-performance liquid chromatography (RP-HPLC). Structural analysis of the peptides showed that β 2-Bern differs at one position from β 1. Thus, Arg-47 in β 1 is substituted by His in β 2-Bern. This exchange, compatible with a one-base mutation, explains all functional differences by altered interactions with the pyrophosphate moiety of the coenzyme. The difference is also structurally identical to that found for another atypical β 2-subunit, the β 2-Oriental type of major Asian occurrence, linking these two atypical forms of human alcohol dehydrogenase. Alcohol dehydrogenase Human liver isoenzyme Primary structure Mutation