Time Dependence of Near-Infrared Spectra of Photodissociated Hemoglobin and Myoglobin

The near-infrared charge-transfer transitions at ~760 nm in photodissociated hemoglobin and myoglobin display very different time dependences. In photodissociated myoglobin at room temperature the transition has fully relaxed to its deoxymyoglobin value by 10 ns. In photodissociated hemoglobin, the transition is shifted by 6 nm to longer wavelengths at 10 ns. It relaxes about halfway back to the deoxyhemoglobin value by about 100 ns but subsequently changes very slowly out to about 100 μs when the signal intensity becomes too small to follow any further. The intensity of this transition, present in only five-coordinate hemes, is found to follow the same time dependence as the wavelength change. Consequently, there appears to be a correlation between a structural property of the heme (as inferred from the wavelength of the charge-transfer transition) and a functional property (the CO recombination) of the protein (as inferred from the intensity of the transition). Possible origins for this correlation are considered.