Knowledge Bank

The photolysis of carbon monoxide hemoglobin by a single 530 nm 6 psec pulse from a mode-locked Nd-glass laser results in a first order excitation rate constant of $1.0\times 1011$ $sec-1$. The Soret band 440 nm photo-dissociation is interpreted as corresponding to electronic-structural changes in the heme which provides the trigger for the binding of ligands. Subsequent recombination of CO and protein structural transformations are monitored by use of a He-Cd laser beam coincident at the sample with the photolysis and Soret interrogation beams. The latter events take place in three distinct time regions depending on excitation pulse energy and pulse rate. Excitation with a single pulse (0.8-4 mJ) results in a relaxation from a transient state to the ground state with first order rate constant of $5\times 103$ $sec-1$. With an attenuated pulse train of approximately 100 pulses (7.5 mJ) a new transient state appears at a later time with a first order rate constant of $66sec-1$. A non-attentuated pulse train (15 mJ) reveals the presence of an intermediate transient state having a life-time of 6 ms. The implication of these rate constants to the Hb-CO dissociation and recombination mechanism will be discussed.Permanent address for