Protein relaxation dynamics in human myoglobin

Transient absorption spectra in the Soret region have been measured following the photolysis of human MbCO in 75%(w/w) glycerokwater at 250,270, and 290 K. The peak of the transient difference spectrum near 436 nm shifts from low to high energy on the nanosecond time scale. The spectral changes are quantitatively analyzed using an approach based on singular value decomposition, and the results are interpreted in terms of a structural relaxation of the protein. The kinetics of the relaxation and hgand rebinding are nonexponential in time. At all three temperatures, the relaxation is complete prior to the end of the geminate phase of recombination. At 250 K the transient spectra have relaxed to the equilibrium deoxyMb-MbCO spectrum after 10 us. At 290 K the relaxation is faster and is complete on the ns time scale. The kinetics of the ge.minate recombination following the spectral changes are single exponential.