PHOTOLYSIS-INDUCED STRUCTURAL-CHANGES IN SINGLE-CRYSTALS OF CARBONMONOXY MYOGLOBIN AT 40 K

Myoglobin's reversible binding of oxygen is a model for studies of pro tein control of ligand binding and discrimination. Protein relaxation and geminate ligand rebinding subsequent to ligand photodissociation h ave keen studied extensively lay a variety of techniques. The ps to ns time scales for these processes are still much shouter than the ms ti me resolution of X-ray diffraction experiments, but it may be possible to trap these intermediates at low temperatures. We report here an X- ray diffraction investigation of structural changes induced by photoly sis of carbonmonoxy myoglobin crystals at 40 K. Our results provide a structural basis for the interpretation of ambient and low temperature spectroscopic observations and molecular dynamics simulations of the ligand photodissociation and binding processes in haem proteins.