For diagram of anaerobic corrin biosynthesis (part 1), click here
CbiG (gene name)
cobalt-precorrin 5A acylhydrolase
This enzyme hydrolyses the ring A acetate δ-lactone of cobalt-precorrin-5A resulting in the loss of the C-20 carbon and its attached methyl group in the form of acetaldehyde. This is a key reaction in the contraction of the porphyrin-type tetrapyrrole ring and its conversion to a corrin ring in the anaerobic (early cobalt insertion) adenosylcobalamin biosynthesis pathway.
Kajiwara, Y., Santander, P.J., Roessner, C.A., Perez, L.M. and Scott, A.I. Genetically engineered synthesis and structural characterization of cobalt-precorrin 5A and -5B, two new intermediates on the anaerobic pathway to vitamin B12: definition of the roles of the CbiF and CbiG enzymes. J. Am. Chem. Soc.128 (2006) 9971–9978. [PMID: 16866557]