Joins adenosylcobinamide-GDP and alpha-ribazole to generate adenosylcobalamin (Ado-cobalamin). Also synthesizes adenosylcobalamin 5'-phosphate from adenosylcobinamide-GDP and alpha-ribazole 5'-phosphate. adenosylcob(III)inamide-GDP + alpha-ribazole = adenosylcob(III)alamin + GMP + H(+) adenosylcob(III)inamide-GDP + alpha-ribazole 5'-phosphate = adenosylcob(III)alamin 5'-phosphate + GMP + H(+) Cofactor biosynthesis; adenosylcobalamin biosynthesis; adenosylcobalamin from cob(II)yrinate a,c-diamide: step 7/7. Associated with a large complex of proteins. Belongs to the CobS family. Was originally thought to originate from Pseudomonas denitrificans, but similarity searches show that the sequence is much closer to Sinorhizobium. The entry's taxonomy has been changed. Extended N-terminus.