Kinetics of polymerization of deoxyhemoglobin S and mixtures of hemoglobin A and hemoglobin S at high hemoglobin concentrations |
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Authors: | GLarry Cottam Michael R Waterman BCecil Thompson |
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Institution: | 1. Department of Biochemistry, The University of Texas Health Science Center at Dallas, Southwestern Medical School, 5323 Harry Hines Boulevard, Dallas, Texas 75235 U.S.A.;2. Department of Physics, University of Texas at Arlington, Arlington, Texas 76010 U.S.A. |
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Abstract: | Transverse water proton relaxation times (T2) have been measured as a function of time after deoxygenation of solutions containing hemoglobin S. The shortened T2 values observed upon deoxygenation of hemoglobin S result from an increase in the correlation time (τc) of the water fraction irrotationally bound to deoxyhemoglobin S as it polymerizes. Therefore, the change in τc as a function of time after deoxygenation can be used to measure the rate of polymer formation. The change in τc observed is reasonably fit by the first-order equation τ = τ0 (1 ? e?kt) + τoxy. At a total hemoglobin concentration of approximately 300 mg/ml, the pseudo-first-order rate constant in a heterozygous AS sample is 25 times slower than in a homozygous S sample, k = 0.019 and 0.47 s?1, respectively. Since the transit time for an erythrocyte in vivo is approximately 15 s, these results suggest that the heterozygous A/S erythrocyte would traverse the circulation and become reoxygenated before extensive polymerization and, therefore, cell sickling could occur. For the homozygous S/S erythrocyte, there is ample time for polymerization and for cell sickling during circulation. |
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