Addition of Co(2+) to culture medium decides the functional expression of a recombinant nitrile hydratase in Escherichia coli.

A nitrile hydratase (NHase) gene from Aurantimonas manganoxydans, cloned and expressed in Escherichia coli, gave an enzyme that efficiently hydrated 3-cyanopyridine to nicotinamide with high thermal stability. We have now found that adding Co(2+) at 0.1 mM to LB medium was essential for production of an active enzyme. However, ≥0.3 mM Co(2+) inhibited the growth of host cells in LB medium and decreased the production of the recombinant NHase. Furthermore, β-mercaptoethanol promoted regeneration of the Co(2+)-defective apoenzyme in vitro possibly by breaking a key disulfide bond thereby promoting the incorporation of Co(2+) into the apoenzyme.