Catalyzes the conversion of precorrin-8X to hydrogenobyrinate. 3 H(+) + precorrin-8X = hydrogenobyrinate Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from precorrin-2 (aerobic route): step 8/10. Belongs to the CobH/CbiC family.