Nanosecond transient Raman spectra of photolysed carboxyhaemoglobin [28]

CONFORMATIONAL CHANGES accompanying the photolysis of carboxyhaemoglobin (CO-Hb) have been the subject of much recent study. It is known from time resolved absorption studies that the process is not simple, comprising various steps on time scales ranging from picoseconds to milliseconds^1-6. Removal of the CO molecule is complete within picoseconds⁵, but the existence of an unknown transient with a 100 ns lifetime has been demonstrated¹. No conclusion has been possible as to the time required for the reorganisation of the porphinato core. In principle, resonance Raman scattering offers a more detailed source of conformational information. From steady state Raman spectra, the normal modes have been identified ^7,8. A clear empirical correlation has been found⁹ between the position of the resonantly enhanced anomalously polarised line in the region 1,550-1,590 cm^-1, and the porphinato core size. Here we report the first nanosecond time-resolved spectra of CO-Hb. From our results it is clear that the main reorganisation of the prophinato core occurs within 5 ns of photolysis.