On the conformation change attending the hydration of lyophilized cytochrome c

When lyophilized cytochrome c is disolved in pH 5 to 9 buffers, a spectroscopic change can be detected with a first‐order rate constant of 0.016 sec⁻¹ at 23°, activation energy of 24.2 kcal/mole and entropy of activation of 11 e.u. The difference spectrum obtained by extrapolating the kinetic plots to zero time indicates that the form obtained by dissolving cytochrome c is in the low spin state and lacks the 695 nm band. It is proposed that the rate process observed corresponds to a conformation change in which the lysyl‐79 residue is displaced from iron coordination by the methionyl‐80 residue.