Adenosyltransferase tailors and delivers coenzyme B12.

The reactivity and relative rarity of most cofactors pose challenges for their delivery to target enzymes. Using kinetic analyses, we demonstrate that adenosyltransferase, which catalyzes the final step in the assimilation of coenzyme B12, directly transfers the cofactor to methylmalonyl coenzyme A mutase. The strategy of using the final enzyme in an assimilation pathway for tailoring a cofactor and delivering it to a dependent enzyme may be general for cofactor trafficking.