Precorrin-6A synthase participates in the pathway toward the biosynthesis of cobalamin (vitamin B12). There are two distinct cobalamin biosynthetic pathways in bacteria. The aerobic pathway requires oxygen, and cobalt is inserted late in the pathway; the anaerobic pathway does not require oxygen, and cobalt insertion is the first committed step towards cobalamin synthesis. This model represents CobF, the precorrin-6A synthase, an enzyme specific to the aerobic pathway. After precorrin-4 is methylated at C-11 by CobM to produce precorrin-5, CobF catalyzes the removal of the extruded acyl group in the subsequent step, and the addition of a methyl group at C-1. The product of this reaction is precorrin-6A, which gets reduced by an NADH-dependent reductase to yield precorrin-6B. This family includes enzymes in GC-rich Gram-positive bacteria, alpha proteobacteria and Pseudomonas-related species.
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