Influence of cobalt substitution on the activity of iron-type nitrile hydratase: are cobalt type nitrile hydratases regulated by carbon monoxide?

Comamonas testosteroni Ni1 nitrile hydratase is a Fe-type nitrile hydratase whose native and recombinant forms are identical. Here, the iron of Ni1 nitrile hydratase was replaced by cobalt using a chaperone based Escherichia coli expression system. Cobalt (CoNi1) and iron (FeNi1) enzymes share identical Vmax (30nmolmin−1mg−1) and Km (200μM) toward their substrate and identical Ki values for the known competitive inhibitors of FeNi1. However, nitrophenols used as inhibitors do display a different inhibition pattern on both enzymes. Furthermore, CoNi1 and FeNi1 are also different in their sensitivity to nitric oxide and carbon monoxide, CO being selective of the cobalt enzyme. These differences are rationalized in relation to the nature of the catalytic metal center in the enzyme.