The enzyme, which participates in the aerobic (late cobalt insertion) pathway of adenosylcobalamin biosynthesis, catalyses the reduction of the double bond between C-18 and C-19 of precorrin-6A. See EC
1.3.1.106, cobalt-precorrin-6A reductase, for the corresponding enzyme that participates in the anaerobic cobalamin biosynthesis pathway.