NONEXPONENTIAL RELAXATION AFTER LIGAND DISSOCIATION FROM MYOGLOBIN - A MOLECULAR-DYNAMICS SIMULATION

Molecular dynamics simulations of myoglobin after ligand photodissocia tion show that the out-of-plane motion of the heme iron has a rapid su bpicosecond phase followed by a slower nonexponential process involvin g more global protein relaxation. Individual trajectories show rather different behavior, suggesting there is an inhomogeneous component to the relaxation. The calculated time dependence of the iron motion over 100 ps is in excellent agreement with the frequency shift of band III of the heme group [see Lim, M., Jackson, T. A. & Anfinrud, P. A. (199 3) Proc. Natl. Acad. Sci. USA 90, 5801-5804]. If that the barrier to r ebinding depends on the out-of-plane iron position, the time dependenc e obtained from the simulation can explain the nonexponential room-tem perature geminate recombination of NO.