COMPLEX NONEXPONENTIAL RELAXATION IN MYOGLOBIN AFTER PHOTODISSOCIATION OF MBCO - MEASUREMENT AND ANALYSIS FROM 2-PS TO 56-MU-S

Photodissociation of carbon monoxide myoglobin (MbCO) creates Mb in a nonequilibrium conformation and triggers a global conformational change. The driving force for this change is localized initially in the iron-porphyrin coordinate. The dynamics of the iron-porphyrin displacement at physiologically relevant temperatures have been followed by probing the evolution of band III, a weak iron-porphyrin charge-transfer transition near 13110 cm-1 (763 nm) that is sensitive to the out-of-plane position of the iron. This functionally important motion is highly nonexponential, stretching over 5 decades in time in 70:30 (w/w) glycerol/water mixtures at 301 +/- 1 K. The relaxation is well described by a stretched exponential function that has been modified to account for the limiting rate associated with the primary relaxation process.