The Role of Lys-228 Residue in Horse Liver Alcohol Dehy-drogenase Activity

Lys-228 in horse liver alcohol dehydrogenase isoenzyme E(HLADH-E) was mutated to glycineby site-directed mutagenesis. The specific activity of the mutant enzyme was increased about 4-fold nad Michaelis constants for $NAD^+(K_a){\;}and{\;}NADH(K_q)$ increased by about 350-and 50-fold, respectively. The wild-type enzyme and K228TG mutant enzyme were treated with ethylacetimidate. Acetimidylation of the wild-type enzyme increased the activity about 10-fold, but the mutant enzyme ws little affected. These results confirm that Lys-228 residue plays an important role in the activity of the enzyme through forming the hydrogen bond with adenosine ribose of $NAD^+$.