Ethanol formation in adh0 mutants reveals the existence of a novel acetaldehyde-reducing activity in Saccharomyces cerevisiae

Abstract

A strain of Saccharomyces cerevisiae has been constructed which is deficient in the four alcohol dehydrogenase (ADH) isozymes known at present. This strain (adho), being irreversibly mutated in the genes ADHI, ADH3, and ADH4 and carrying a point mutation in the gene ADH2 coding for the glucose-repressible isozyme ADHII, still produces up to one third of the theoretical maximum yield of ethanol in a homofermentative conversion of glucose to ethanol. Analysis of the glucose metabolism of adho cells shows that the lack of all known ADH isozymes results in the formation of glycerol as a major fermentation product, accompanied by a significant production of acetaldehyde and acetate. Treatment of glucose-growing adho cells with the respiratory-chain inhibitor antimycin A leads to an immediate cessation of ethanol production, demonstrating that ethanol production in adho cells is dependent on mitochondrial electron -transport. Reduction of acetaldehyde to ethanol in isolated mitochondria could also be demonstrated. This reduction is apparently linked to the oxidation of acetaldehyde to acetate. Preliminary data suggest that this novel type of ethanol formation in S. cerevisiae is associated with the inner mitochondrial membrane.

Microbial Synergy via an Ethanol-Triggered Pathway

“…ADH3 is a mitochondrial isozyme of alcohol dehydrogenase (42). ADH4 is a formaldehyde dehydrogenase and has no effect on ethanol production (8). Therefore, ADH2 and ADH4 were not disrupted.…”

Biochemical basis of mitochondrial acetaldehyde dismutation in Saccharomyces cerevisiae

“…Despite this requirement for a functional respiratory chain in adhi mutants, glucose is largely converted to the major fermentation products, glycerol and ethanol, and to minor products such as acetaldehyde and acetate. We showed recently that the residual ethanol production in adhl mutant cells (approximately 30% of wild-type level) cannot be attributed to any of the known ADH isozymes (ADH II through ADH IV) by using mutant cells carrying null alleles at the four ADH loci (9). The existence of another cytoplasmic NAD+-dependent ADH isozyme was also ruled out since adh°cells cannot grow in a medium containing ethanol as the sole source of carbon.…”

Metabolic engineering of Saccharomyces cerevisiae to improve succinic acid production based on metabolic profiling

“…52) Moreover, when the ethanol biosynthesis pathways are disrupted, glycerol biosynthesis is induced to oxidize NADH produced through glycolysis. 53,54) Hence, in our experiments, glycerol production was increased in ADH1-5-disrupted strains S149 and S149sdh12.…”