ABSTRACT
Significant differences were observed in the zymogram patterns of NAD(+)-dependent ethanol dehydrogenase and acetoin dehydrogenase activity in seven strains of brewer's yeast examined by non-denaturing PAGE. Bottom-fermenting (lager) strains contained quite different activity bands of acetoin dehydrogenase activity compared with top-fermenting (ale) strains. These differences were confirmed when cell-free extracts of ale yeasts were heated at 55 degrees C. This destroyed most of the diacetyl reductase activity, while leaving acetaldehyde reductase and other reductase activities unaffected. In contrast, heating cell-free extracts of lager yeasts at 55 degrees C inactivated diacetyl reductase activity and the other reductase activities at the same rate, and more slowly than with ale strains. Similar distinctions between the two types of yeast could be made by examining the effect of heat on the ratio (activity of the various substrates with NADH as electron donor)/(activity with reduced acetylpyridine-adenine dinucleotide as electron donor). The data show that the acetoin dehydrogenase/diacetyl reductase enzyme present in ale-yeast strains differs in mobility and heat-stability from that of larger strains, and that both can be distinguished from the major alcohol dehydrogenase activity bands.
