Simulation of carboxymyoglobin photodissociation.

The structures of deoxymyoglobin and CO-bound myoglobin show that the CO molecule is not packed so tightly by the distal pocket amino acid residues to prevent its motion away from the iron atom upon photodissociation. Simulations of low temperature photodissociation by energy minimization techniques show that the CO moves to a position ~ 4Angstroms away from the iron atom due to the van der waals forces. The simulations are consistent with the inferences, drawn from spectroscopic data on photodissociated myoglobin, that the CO molecule is electronically fully separated from the iron atom but inconsistent with conclusions, drawn from EXAFS data, which place the photodissociated CO molecule at covalent bond distances from the iron atom.