Dimerization of multiple maize ADHs studied in vivo and in vitro

Anaerobically induced primary roots simultaneously express two alcohol dehydrogenase (Adh) genes which specify three types of electrophoretically separable dimers: Set I, II, and III ADH. The S inbred line yields a particular activity ratio among these three sets. By use of an Adh ₁ ^null mutant allele and in vitro chemical dissociation and reassociation of ADH dimers, these studies extrapolate from an ADH activity ratio to the actual ratio of ADH protein. Conclusions are that (1) ADH₁ and ADH₂ promoters dimerize randomly in vivo and in vitro, (2) the heterodimeric isozyme (Set II) is approximately the enzymological sum of its subunits under these assay conditions, and (3) ADH-2 subunits are from 10 to 20% as active as ADH₁ subunits under these assay conditions. These conclusions imply that the unlinked Adh genes are coordinately regulated and reconfirm the two-gene-three-dimer model for the maize ADH isozymes.