Reduction of Cobamides by Reduced Ferredoxin

Reduced ferredoxin is capable of reducing nonenzymatically cyano-B12. Spectral studies have shown that B12r (a 1-electron reduced derivative of the vitamin) accumulates in the reaction although the formation of methyl-B12 was observed upon the addition of methyl iodide to the incubation. The data indicate that reduction of cyano-B12 by reduced ferredoxin results in the transient formation of B12s (a 2-electron reduced derivative), which is not stable under the conditions used, and oxidizes to the more stable B12r. Reduced ferredoxin is able to supply the reducing-capability necessary for the enzymatic conversion of cyano-B12 to deoxyadenosyl-B12.