Date of this Version
This year marks the one hundredth anniversary of the first observation of CO photodissociation from HbCO, with the correct interpretation and publication following in the next year (Haldane and Smith, 1896). Little of kinetic importance could be learned from this photosensitivity, however, until the development of sensitive photodetectors and short duration high intensity light sources. These allowed Gibson, in pioneering discoveries in the mid to late 1950's (Gibson, 1956, 1959), to discover “Hb*,” a rapidly reacting form of hemoglobin, which we now associate with deoxy Hb in the tertiary relaxed “r” 9 state with the protein in the quaternary R state. Because this state was not readily accessible by rapid mixing experiments, photolysis was needed to generate the reactant. It became clear that cooperative binding of CO was largely manifested through changes in the association rate constant. Photolysis also allowed Gibson to make what were probably the first precise measurements of the rate of a conformational change in a native protein, the R--T transition in hemoglobin (Gibson, 1959).