Fig. 4.

(A) Minimal scheme of geminate recombination phases of CO starting from the MV¹-CO and R-CO states. Two different configurations of dissociated CO in the protein (d^red……CO_i i=I, II) are required to explain the two geminate recombination phases. The ratio of forward and backward rates from these configurations is roughly estimated from the amplitudes of the phases; the sums of the rates correspond to the experimentally observed rates. The state (d_red + CO) denotes a state where CO has escaped from the protein. In this minimal scheme, if heme b₅₉₅ is reduced prior to dissociation of the heme d-CO bond, geminate recombination from the (d_red……CO_I) state does not compete efficiently with population of the (d^red……CO_II) state. (B) Minimal scheme of bimolecular CO recombination and electron transfer starting from the MV¹-CO. The first dissociation step comprises all steps in scheme (A). The ratio of forward and backward rates from the CO dissociated d_red is roughly estimated from the amplitudes of the phases; the sums of the rates correspond to the experimentally observed rates.