Biochemistry and Cell Biology
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Browsing Biochemistry and Cell Biology by Author "Anfinrud, Philip A."
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Item Real-time tracking of CO migration and binding in the ? and ? subunits of human hemoglobin via 150-ps time-resolved Laue crystallography(Elsevier, 2013) Schotte, Friedrich; Cho, Hyun Sun; Soman, Jayashree; Wulff, Michael; Olson, John S.; Anfinrud, Philip A.; W.M. Keck Center for Computational BiologyWe have developed the method of picosecond Laue crystallography and used this capability to probe ligand dynamics in tetrameric R-state hemoglobin (Hb). Time-resolved, 2 Å-resolution electron density maps of photolyzed HbCO reveal the time-dependent population of CO in the binding (A) and primary docking (B) sites of both α and β subunits from 100 ps to 10 μs. The proximity of the B site in the β subunit is about 0.25 Å closer to its A binding site, and its kBA rebinding rate (∼300 μs−1) is six times faster, suggesting distal control of the rebinding dynamics. Geminate rebinding in the β subunit exhibits both prompt and delayed geminate phases. We developed a microscopic model to quantitatively explain the observed kinetics, with three states for the α subunit and four states for the β subunit. This model provides a consistent framework for interpreting rebinding kinetics reported in prior studies of both HbCO and HbO2.