FIRST RESULTS ON A MODIFIED ADH 1 OBTAINED FROM SACCHAROMYCES CEREVISIAE GROWN IN EXCESS OF COBALT.

Yeast cells of Saccharomyces cerevisiae incorporate cobalt in alcohol dehydrogenase (ADH) when grown in increasing concentrations of this metal. The substitution zinc-cobalt in the enzyme originates a new ADH form. A ratio cobalt:zinc 1:4 was determined. The modified enzyme extracted from a 6 mM CoCl2 medium still retained its enzymatic activity while for higher molar concentrations only a low activity can be detected. Cobalt ADH (from a 4 mM CoCl2 yeast culture) displayed higher specific activity (30-50 fold) as compared to the native ADH. A good resistance to high temperatures (>60-degrees-C) and to pH values in the alkaline range (pH=10) was observed. Lineweaver-Burk plots indicate a random bi-bi mechanism of reaction, different from that of the native zinc-enzyme (ordered bi-bi). We assume that the introduction of cobalt into the enzymatic molecule could alter the affinity of ADH for its ligands, resulting in better catalytic properties.