TIME-RESOLVED STEP-SCAN FT-IR SPECTROSCOPY OF THE PHOTODYNAMICS OF CARBONMONOXYMYOGLOBIN

The kinetics of protein response and of CO recombination after photoly sis of the Fe-CO bond in carbonmonoxymyoglobin have been monitored via time-resolved step-scan FT-IR absorption difference spectroscopy in D 2O solution. Although the initial photodissociation is too fast to obs erve with currently available FT-IR instrumentation, we have been able to correlate the CO recombination kinetics with protein secondary str uctural changes via changes in the amide I band of the polypeptide cha in with microsecond time resolution. The spectral and kinetic data cor roborate and confirm previously published single-frequency infrared st udies. This is the first application of time-resolved step-scan FT-IR spectroscopy in the absorbance difference mode to study the photodynam ics of an aqueous protein solution at room temperature. This work also demonstrates the potential of the technique for the sub-microsecond k inetic analysis of other biological molecules of interest.