The kinetics of conformational changes in hemoglobin, studied by laser photolysis

Photolysis of carbon monoxide and oxygen derivatives of hemoglobin by a short laser pulse produces a transient species that rapidly decays to normal deoxyhemoglobin. The effect, which is also observed on single chain proteins and on noncooperative aggregated forms, has been interpreted as corresponding to structural changes in the heme pocket on ligand dissociation. The decay of the transient species follows first-order kinetics with constants ranging from 0.8 to 1.8 x 10(7) sec(-1). In cooperative hemoglobins, the kinetic constants are pH-dependent, though remaining first- or pseudo first-order at all wavelengths. This shows the close linkage of tertiary and quaternary structure changes in normal hemoglobin.