Biochemical basis of mitochondrial acetaldehyde dismutation in Saccharomyces cerevisiae.

As reported previously, Saccharomyces cerevisiae cells deficient in all four known genes coding for alcohol dehydrogenases (ADH1 through ADH4) produce considerable amounts of ethanol during aerobic growth on glucose. It has been suggested that ethanol production in such adh0 cells is a corollary of acetaldehyde dismutation in mitochondria. This could be substantiated further by showing that mitochondrial ethanol formation requires functional electron transport, while the proton gradient or oxidative phosphorylation does not interfere with reduction of acetaldehyde in isolated mitochondria. This acetaldehyde-reducing activity is different from classical alcohol dehydrogenases in that it is associated with the inner mitochondrial membrane and also is unable to carry out ethanol oxidation. The putative cofactor is NADH + H+ generated by a soluble, matrix-located aldehyde dehydrogenase upon acetaldehyde oxidation to acetate. This enzyme has been purified from mitochondria of glucose-grown cells. It is clearly different from the known mitochondrial aldehyde dehydrogenase, which is absent in glucose-grown cells. Both acetaldehyde-reducing and acetaldehyde-oxidizing activities are also present in the mitochondrial fraction of fermentation-proficient (ADH+) cells. Mitochondrial acetaldehyde dismutation may have some significance in the removal of surplus acetaldehyde and in the formation of acetate in mitochondria during aerobic glucose fermentation.