Human liver alcohol dehydrogenase: the unique properties of the "atypical" isoenzyme beta 2 beta 2-Bern can be explained by a single base mutation.

Two allelic variant alcohol dehydrogenase isoenzymes, beta 2 beta 2-Bern and beta 1 beta 1, coded by the ADH2 locus, were isolated from human livers of Caucasian origin. They represent the "atypical" and "typical" phenotype, respectively. beta 2 beta 2-Bern has a higher specific activity and a lower pH-optimum, has a higher kM for NAD+, is less susceptible to inactivation by iodoacetate, and cannot be activated with chloride ions. In order to define the structural basis for these properties, we determined the amino acid sequence difference between the beta 2-Bern and the beta 1 polypeptide chains. Peptides were prepared by cleavages with trypsin and CNBr, and were purified by exclusion chromatography and reverse phase high performance liquid chromatography. The structural analysis showed that beta 2-Bern differs at only one position from beta 1: Arg-47 in beta 1 is substituted for His-47 in beta 2-Bern. This exchange, which is identical to that reported for the beta 2-Oriental chain, alters the binding of the pyrophosphate group of the coenzyme NAD(H), and also that of iodoacetate, thus explaining the observed differences between beta 2 beta 2-Bern and beta 1 beta 1.