Mechanism of Action of Vitamin Bn. A New Test for Free Radical Intermediates Using a Cyclopropane Model for the Methylmalonyl-CoA to Succinyl-CoA Carbon Skeleton Rearrangement

摘要

In recent years, evidence has emerged of the involvement of free radicals in the coenzyme B_(12)-dependent carbon skeleton rearrangement reactions. However, the rearrangements promoted by coenzyme B_(12) are multistep sequences, and it continues to beworthwhile to ask whether nonradical steps accompany the radical reactions. We have shown for a model of the methylmalonyl-CoA carbon skeleton rearrangement that no radical intermediates are trapped by a pendant 4-pentenyl side chain. Accordingly, the permissible lifetime of any radical intermediate associated with the model rearrangement must then be not greater than 10~(-5) s, corresponding to the rate of cyclization of the 5-hexenyl radical.