Dynamics of Structure and Energy of Horse Carboxymyoglobin after Photodissociation of Carbon Monoxide

Abstract

The energetics and structural volume changes after photodissociation of carboxymyoglobin are quantitatively investigated by laser-induced transient grating (TG) and photoacoustic calorimetric techniques. Various origins of the TG signal are distinguished: the phase grating signals due to temperature change, due to absorption spectrum change, and due to volume change. We found a new kinetics of approximately 700 ns (at room temperature), which was not observed by the flash photolysis technique. This kinetics should be attributed to the intermediate between the geminate pair and the fully dissociated state. The enthalpy of an intermediate species is determined to be 61 +/- 10 kJ/mol, which is smaller than the expected Fe-CO bond energy. The volume of MbCO slightly contracts (5 +/- 3 cm(3)/mol) during this process. CO is fully released from the protein by an exponential kinetics from 25 to -2 degrees C. During this escaping process, the volume expands by 14.7 +/- 2 cm(3)/mol at room temperature and 14 +/- 10 kJ/mol is released, which should represent the protein relaxation and the solvation of the CO (the enthalpy of this final state is 47 +/- 10 kJ/mol). A potential barrier between the intermediate and the fully dissociated state is DeltaH(*) = 41.3 kJ/mol and DeltaS(*) = 13.6 J mol(-1) K(-1). The TG experiment under a high wavenumber reveals that the volume expansion depends on the temperature from 25 to -2 degrees C. The volume changes and the energies of the intermediate species are discussed.

Protein structural dynamics in solution unveiled via 100-ps time-resolved x-ray scattering

“…4C around 1 μs corresponds to departure of CO from the protein into the surrounding solvent. The timescale for this departure is similar to that reported using transient grating techniques (26,27). The integrated SAXS feature also appears to be sensitive to ligand migration to other internal cavities in the protein.…”

Diffractive optics-based heterodyne-detected four-wave mixing signals of protein motion: From “protein quakes” to ligand escape for myoglobin

“…31-33), previous work from this lab (22), and the recent grating studies of Terazima and his colleagues (also Ϸ700 ns; ref. 34). The use of heterodyne detection and extended dynamic range has enabled the resolution of the CO motion through the protein, notably the distinctive plateau region in the CO escape statistics.…”

Functional Nanohybrid Materials from Photosynthetic Reaction Center Proteins

“…It must be noted that the whole photocycle is under intensive discussion in the literature and outside the scope of the present publication. Figure 6 provides representative examples of changes in light-induced transient absorption and grating (this later is proportional with the square of the change in the refractive index) under different sample preparations [20,69,70]. It must be mentioned that in addition to the examples presented here, fine-tuning of lifetimes can be achieved from sub-ps to s time scales by either genetic engineering or postmodification of the protein structure.…”