Figure 2.

Simplified schematic diagram of the states and pathways of formation following photolysis of AdoCbl in solution and in holo-EAL. The cobalt in cobalamin and the C5′-methylene center in the 5′-deoxyadenosyl moiety are represented, as follows: [Co^III-C], intact coenzyme; [Co^III-C]*, excited singlet state; [Co^{II •}C]_gem, geminate radical pair; Co^{II •}C, cage escaped radical pair. Intermediate excited and relaxed states,^27,32 which are not shown, are represented by the sequence of arrows leading from [Co^III-C]*. Rate constants are defined as follows: k_r, excited state to ground state relaxation; k_gr, geminate recombination; k_ce, cage escape; k_cer, reformation of geminate radical pair from cage escaped radical pair. The subscript, i, refers to three different cage escaped photoproduct radical pair species, P_i, that were identified in holo-EAL.²⁶