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A linear criterion testing the applicability of the Monod-Wyman-Changeux(MWC) mechanism characterizing,at a single effector con-centration,concerted allosteric transitions plots log {[α-v_r(1+α)]/[v_r(1+cα)-cα]} against log[(1+cα)/(1+α)],with a slope of (n-1)andintercept of log L.(Here v_r is the relative velocity or,in bind-ing experiments,the fractional binding,α the substrate concentra-tion relative to the smallest conformational dissociation constantK_R,L the constant for the conformational equilibrium,c=K_R/K_Tthe ratio of conformational dissociation constants,and n the de-gree of the rate or binding function).The plot is applied to theexperiments of Roughton and Lyster [Hvalradets Skrifter,48,185-198,(1965)] on the binding of oxggen to human hemoglobin.At pH7.0 the data are in agreement with the predictions of the MWC-mechanism.This conclusion is confirmed by weighted nonlinear re-gression analysis which yields a statistically not significantlack of fit,random weighted residuals,and parameters which agreeclosely with those obtained from the graphical analysis.At pH 9.1the MWC-mechanism is not applicable.At either pH the experimentsdo not support the suitability of the sequential binding mechanismeither with square or tetrahedral geometry.
A linear criterion testing the applicability of the Monod-Wyman-Changeux (MWC) mechanism characterizing, at a single effector con-centration, concerted allosteric transitions plots log {[α-v_r (1 + α)] / [v_r ) -cα]} against log [(1 + cα) / (1 + α)], with a slope of (n-1) andintercept of log L. (Here v_r is the relative velocity or, in bind- ing experiments, the fractional binding, α the substrate concentra tion relative to the smallest conformational dissociation constant K_R, L the constant for the conformational equilibrium, c = K_R / K_T the ratio of conformational dissociation constants, and n the de-gree of the rate or binding function, The plot is applied to the experiments of Roughton and Lyster [Hvalradets Skrifter, 48, 185-198, (1965)] on the binding of oxggen to human hemoglobin. At pH 7.0 the data are in agreement with the predictions of the MWC-mechanism. This conclusion is confirmed by weighted nonlinear re-gression analysis which results in a significant not significant fit, random weighted res iduals, and parameters which agreeclosely with those obtained from the graphical analysis. At pH 9.1the MWC-mechanism is not applicable. At either pH the experiments do not support the suitability of the sequential binding mechanismeither with square or tetrahedral geometry.