Properties of a cobalt-reactivated form of yeast alcohol dehydrogenase

Yeast alcohol dehydrogenase (Y-ADH) is a widely studied metal-enzyme for its well-known biotechnological importance. Although its structure has been extensively investigated, some topics still remain controversial (zinc content and role), and various attempts aiming at modifying its structure to improve its catalytic properties have been made. In this paper, a metal-substituted Y-ADH has been prepared in vitro, in which one Zn atom per molecule (only one of those directly involved in catalysis) has been substituted by one Co atom. The substitution was obtained through zinc removal by a chelating treatment (with Chelex 100) followed by cobalt insertion. The zinc content in the native enzyme was preliminarily evaluated (taking care to avoid contamination) to be 4.1±0.1 g-at./molecule. After cobalt substitution, the ratio Zn:Co in the enzyme results to be 3:1. The active Co-Y-ADH has been compared with the native enzyme: it has lower specific activity (about 50%) and lower substrate affinity but greater thermo-resistance and a pH stability in a wider range than the native Y-ADH. A similar behavior, as far as cobalt content, thermo-resistance and pH stability are concerned, but greater specific activity and substrate affinity, were shown by an in vivo-substituted Co-Y-ADH obtained in a previous study.