Heterolysis coenzyme

The radical mechanism involves homolysis of the Co—C bond and the ionic mechanism involves heterolysis of this bond. Since coenzyme Bjj has both Co(II) and Co(I) derivatives, either of these mechanisms is chemically reasonable. The radical pathway provides low-spin Co(II) which is EPR active and therefore easily detectable. However, detection alone does not prove that this is the catalytic pathway. It should be noted that an important function of the protein in these systems is to constrain and protect reactive intermediates and inhibit unwanted side reactions. For example, the substrate radical or anion might combine with the cobalt to give an organocobalt complex as the product of the second step in both reactions (8.13) and (8.14). 

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