Catalytic properties of alcohol dehydrogenase isozymes specified by duplicate genes in the diploid plant Stephanomeria exigua.

The alcohol dehydrogenase (ADH) isozymes induced in flooded roots of the diploid plant Stephanomeria exigua are specified by tightly linked genes comprising a complex locus, Adh1. Individuals homozygous for a complex with two active genes which specify electrophoretically different subunits have three ADH-1 isozymes, two intragenic homodimers and an intergenic heterodimer. Individual isozymes were partially purified from plants homozygous for several different Adh1 complexes and apparent Km values for acetaldehyde, ethanol, NAD, and NADH and responses to temperature, pH, and two different alcohols were determined. The two homodimeric enzymes specified by a particular Adh1 complex generally differed in one or more of the properties studied, and in three of four cases, intergenic heterodimers differed significantly from intermediacy, often having lower Km values than either homodimer. None of the isozymes studied could be considered greatly divergent or defective. Constraints on evolution of duplicate genes which form intergenic heterodimers are considered.