This is family of Colbalmin-5-phosphate synthases, CobS, from bacteria. The CobS enzyme catalyses the synthesis of AdoCbl-5'-p from AdoCbi-GDP and alpha-ribazole-5'-P [1]. This enzyme is involved in the cobalamin (vitamin B12) biosynthesis pathway in particular the nucleotide loop assembly stage in conjunction with CobC, CobU and CobT [1].

1: In vitro synthesis of the nucleotide loop of cobalamin by Salmonella typhimurium enzymes. Maggio-Hall LA, Escalante-Semerena JC; Proc Natl Acad Sci U S A 1999;96:11798-11803. PMID:10518530

2: Characterization of the cobalamin (vitamin B12) biosynthetic genes of Salmonella typhimurium. Roth JR, Lawrence JG, Rubenfield M, Kieffer-Higgins S, Church GM; J Bacteriol 1993;175:3303-3316. PMID:8501034