NONEXPONENTIAL PROTEIN RELAXATION - DYNAMICS OF CONFORMATIONAL CHANGEIN MYOGLOBIN

The picosecond evolution of the tertiary conformation of myoglobin (Mb ) after photodissociation of MbCO was investigated at room temperature by probing band III, a weak iron-porphyrin charge-transfer transition near 13,110 cm-1 (763 nm) that is sensitive to the out-of-plane displ acement of the iron. Upon photolysis, the iron moves out of the plane of the porphyrin, causing a blue-shift of band III and a concomitant c hange in the protein conformation. The dynamics for this functionally important motion are highly nonexponential, in agreement with recent m olecular dynamics simulations [Kuczera, K., Lambry, J.-C., Martin, J.- L. & Karplus, M. (1993) Proc. Natl. Acad. Sci. USA 90, 5805-5807]. The conformational change likely affects the height of the barrier to lig and rebinding and may explain nonexponential NO rebinding.