Developmental and environmental influences in the production of a single NAD-dependent fermentative alcohol dehydrogenase by the zygomycete Mucor rouxii

A soluble NAD-dependent alcohol dehydrogenase (ADH) activity was detected i n mycelium and yeast cells of wild-type Mucor rouxii. In the mycelium of ce lls grown in the absence of oxygen, the enzyme activity was high, whereas i n yeast cells, ADH activity was high regardless of the presence or absence of oxygen. The enzyme from aerobically or anaerobically grown mycelium or y east cells exhibited a similar optimum pH for the oxidation of ethanol to a cetaldehyde (similar to pH 8.5) and for the reduction of acetaldehyde to et hanol (similar to pH 7.5). Zymogram analysis conducted with cell-free extra cts of the wild-type and an alcohol-dehydrogenase-deficient mutant strain i ndicated the existence of a single ADH enzyme that was independent of the d evelopmental stage of dimorphism, the growth atmosphere, or the carbon sour ce in the growth medium. Purified ADH from aerobically grown mycelium was f ound to be a tetramer consisting of subunits of 43 kDa. The enzyme oxidized primary and secondary alcohols, although much higher activity was displaye d with primary alcohols. K-m values obtained for acetaldehyde, ethanol, NAD H(2), and NAD(+) indicated that physiologically the enzyme works mainly in the reduction of acetaldehyde to ethanol.