Question

It has been observed that cells lacking alcohol dehydrogenase accumulate large amounts of glycerol during anaerobic fermentation. Explain why.

Answer 1

As already stated, during anaerobiosis, reoxidation of most NADH is carried out in yeasts by alcohol dehydro-genase. However, production of glycerol under anaerobic conditions is a secondary, but important, way to regener-ate NAD. In S. cerevisiae, mutants lacking alcohol dehydrogenase, still produce ethanol, but in-crease their glycerol production during glucose fermentation . The situation is di¡erent in K. lactis, where a mutant lacking alcohol dehydrogenase activity did not accumulate much glycerol. Glyce rol production plays another important role, namely it allows adaptation of the yeast to situations of osmotic stress. Glycerol formation requires the sequential action of a NADH glycerophosphate dehydrogenase and a glycero-phosphatase.