This enzyme, which forms part of the aerobic (late cobalt insertion) cobalamin biosynthesis pathway, is a type I chelatase, being heterotrimeric and ATP-dependent. It comprises two components, one of which corresponds to CobN and the other is composed of two polypeptides, specified by cobS and cobT in Pseudomonas denitrificans, and named CobST [1]. Hydrogenobyrinate is a very poor substrate. ATP can be replaced by dATP or CTP but the reaction proceeds more slowly. CobN exhibits a high affinity for hydrogenobyrinate a,c-diamide. The oligomeric protein CobST possesses at least one sulfhydryl group that is essential for ATP-binding. See EC
4.99.1.3, sirohydrochlorin cobaltochelatase, for the cobaltochelatase that participates in the anaerobic cobalamin biosynthesis pathway.