Single Polymer Chain

CO binds at a cluster Fe that is bridged to the Ni. Methyl transfer to the Ni is then followed by attack on the bound CO, forming an acetyl adduct, which might migrate from Fe to Ni. Transfer of the acetyl group to CoA completes the catalytic cycle. Alkyl attack on metalbound CO is a well-precedented organometallic process that has been extensively studied (21). Usually the CO binds to the same metal atom that bears the alkyl group, following dissociation of another ligand. In the mechanism suggested in Fig. 3, the function of the Fe-S cluster is to provide access to CO at ambient temperature and pressure, by way of a binding site that is under redox control. Removal of an electron from a metal center has been found to strongly promote the CO insertion reaction (22). Thus, reoxidation of the Fe4S4 cluster in center A could accelerate acetyl formation. There is evidence for acceleration of the CO-acetyl-CoA exchange reaction upon addition of one-electron oxidants (12). 23.