Properties and functional significance of Saccharomyces cerevisiae ADHVI.

The completion of the Saccharomyces cerevisiae genome project has provided the opportunity to explore for new genes of the medium-chain dehydrogenase/reductase enzyme superfamily. Our group has recently identified a new gene, the YMR318C open reading frame, which coded for a Zn-containing NADP(H)-dependent alcohol dehydrogenase (ADHVI). ADHVI has been purified to homogeneity from over expressing yeast cells, and found to be a homodimer of 40 kDa subunits. The enzyme showed a strict specificity for NADP(H) and high activity with a variety of long chain aliphatic and bulky substrates. Aldehydes exhibited 50-12000 times higher catalytic efficiency than the corresponding alcohols. Substrates with high k(cat)/K(m) were: pentanal, veratraldehyde and cinnamaldehyde. The ADHVI expression was strongly induced when galactose was the sole carbon source in the culture medium. Phylogenetic trees include ADHVI in the cinnamyl alcohol dehydrogenase (CADH) family. In contrast to the plant CADH, involved in lignin biosynthesis, this is not the function for ADHVI, since yeast does not synthesize lignin. ADHVI may be physiologically involved in several steps of the lignin degradation pathway, initiated by other microorganisms, in the synthesis of fusel alcohols, products derived from the aminoacidic metabolism, and in the homeostasis of NADP(H). Disruption of ADH6 was not lethal for the yeast, under laboratory conditions.