Reduction of Cobamides by Reduced Ferredoxin

From the ¹ From the Laboratory of Clinical Biochemistry and Experimental Therapeutics Branch, National Heart Institute, and Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20014

Reduced ferredoxin is capable of reducing nonenzymatically cyano-B₁₂. Spectral studies have shown that B_12r (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 B_12s (a 2-electron reduced derivative), which is not stable under the conditions used, and oxidizes to the more stable B_12r.

Reduced ferredoxin is able to supply the reducing-capability necessary for the enzymatic conversion of cyano-B₁₂ to deoxyadenosyl-B₁₂.

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