Hemoglobin ( Hb) as the allosteric protein, in photo -dissociations of liganded Hb has been studied widely. T he mechanisms describing the cooperative binding of CO and other ligands to hemoglobins has been the
subject of extensive studies as an important fundamental problem for a long time. In this paper, the quantum yields in photolyses of carboxy -hemoglobins ( HbCO) of mammals, such as human,
pig, bovine, horse and rabbit, are investigated by the optical pump -probe technique, in which the quantum yield is defined as the molecular number of photoproduct species divided by the absorbed photon number. In the optical
pump -probe technique, the HbCO of the mammals are irradiated by a pulsed pumping laser beam with the wavelength 532 nm, pulse width 8 ns and the repetition frequency 10 Hz, then the HbCO is photo -dissociated.
Meanwhile, another continuous optical beam with the wavelength 432 nm is used as a probe beam to detect the absorbance change induced by the photo -dissociation before and after the laser pulse illuminating HbCO. In the
experiments, a solution with the recognized quantum yield 0 is taken as a standard solution, and adjust the optical absorption ( at the wavelength 532 nm) of the measured solutions to be the same data as that of the standard
solution, then the quantum yield of the measured solution can be obtained by comparing the variations of the optical absorption ( at 432 nm) induced by the photolyses of the solutions with those of the standard solution
measured at the same experimental conditions. The measured results show that the quantum yields o the photolyses of the HbCO are different for varies
mammals, but for three of the mammals, i. e. , pig, bovine and horse, the photolysis quantum yields of their HbCO are very close. However, for the HbCO of rabbit, the quantum yield is much smaller than the others. Finally, the
results are analyzed and discussed. To explain the differences among them, some analyses and discussions on the differences of the amino acid sequences of the five Hb, and the tetramer structures, as well as the salt bridges and
hydrogen bonds between subunits of HbCO among the five mammals are presented.
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