Equilibria and Substrate Specificity Studies with Alcohol Dehydrogenases

Abstract

Abstract While secondary alcohols and NAD+, and ketones and NADH react much slowly than the ethanol–acetaldehyde system in the presence of yeast and liver alcohol dehydrogenases, by starting near equilibrium concentrations, it has been shown that expected thermodynamic equilibria are obtained. With liver ADH, cycloalkanols are remarkably reactive, while with yeast ADH those with six or more carbon atoms in the ring are unreactive. Horse liver ADH shows stereospecificity for 2-octanol, but no stereospecificity for 2-butanol. On the other hand, yeast ADH shows the same stereoselectivity for both alcohols. In the presence of yeast ADH, R(−)-isomers of 2-butanol, 2-octanol and 1-methoxy-2-propanol are not reactive, comparing to the big reactivity of S(+)-isomers of these alcohols, but R(−)-isomer of propylene glycol is also slightly reactive as S(+)-isomer. Further, the reactivity of secondary alcohols with NAD+ in the presence of liver ADH is following, 2-octanol>2-butanol>2-propanol. These results suggest that horse liver ADH is much less sterically hindered at its active site than yeast ADH and that not only the steric factor but also hydrophobic bonding between the end alkyl group of alcohol and the hydrophobic region of enzyme might be another important factor to determine stereospecificity and reactivity of enzyme.