Stereochemistry with Respect to the Substrate

As shown above, the prochiral hydrogens in NADH are clearly differentiated by an ADH system. At the same time, the enzyme recognizes the prochiral hydrogens in ethanol to be transferred. The absolute stereochemical course with respect to the substrate was 

it has been proved that an ADH catalyzes the redox reaction between acetaldehyde and ethanol stereospecifically and that both YADH and HLADH exhibit the same specificity toward the coenzyme and the substrate. These two enzymes can also catalyze the reduction of other aldehydes. It has been ascertained that these reactions 

---