Isokinetic relationships for the effect of inorganic phosphate adn protons on the deoxygenation rate of human hemoglobin
✍ Scribed by J. Mitchell Salhany
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1973
- Tongue
- English
- Weight
- 536 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Abstract
The rate of hemoglobin deoxygenation is measured as a function of inorganic phosphate concentration, pH, and temperature. Isokinetic relationships (enthalpy‐entropy compensation) are searched for by applying the method of O. Exner and, for comparative purposes, the conventional method of plotting the energy of activation (E*) versus the natural log of the pre‐exponentional factor of the Arrhenious equation (In A). Both plots indicate compensation between the activation parameters. However, unlike the conventional plot, the Exner treatment is able to distinguish between two types of compensation. Furthermore, when extrapolated rate constants based on all the data in an Exner plot are transposed into E* vs. In A plots, so‐called “turn‐around” behavior is predicted for the effect of increasing phosphate concentration at constant pH. Such “turn‐around” behavior in E* vs. In A plots has been observed experimentally by Beetlestone and co‐workers for anion binding to human hemoglobin as a functin of pH. Lastly, the compensation temperatures obtained from these data all fall within the Vaslow‐Doherty compensation range (250–350°K) which is thought to indicate that the solvent, water, is involved in the reaction mechanism. Thus, Exner plots appear to further resolve isokinetic temperatures of the Vaslow‐Doherty type. Differences in the electrostriction of solvent in the activated state is suggested as one possible physical source for the Vaslow‐Doherty type compensation observed in this work.