Hill plots hemoglobin

Linked-function mechanisms for cooperative binding interaction of metabolites and/or drugs, based on the presence of two or more different conformational states of the protein or receptor. See Adair Equation Cooperative Ligand Binding Hemoglobin Hill Equation Plot Koshland-Nemethy-Filmer Model Monod-Wyman-Changeux Model Negative Cooperativity Positive Cooperativity... 

Fig. 2. Hill plot for oxygenation of human hemoglobin A as a function of the partial pressure (PO2) of molecular oxygen. The diagram at the right shows that the Hill coefficient will reach a limiting value of one at both extremes of ligand concentration. For this reason this cooperativity index is best measured at ligand concentrations near half-maximal saturation.

Hill plots for myoglobin and hemoglobin are given in Figure 5-14. 

Fig. 53. Oxygen equilibrium curves of cross-linked mixed-valency hybrid hemoglobin (a + CN3)A(ap)cXL, in 0.1 M phosphate plus 2 mM KCN at various pH values. (A) Hill plots (B) 02 binding constants. [From Miura et al. (1987)].

This means that the value of P50 may be determined from the Hill plot s y intercept or x inercept. For example, the y intercept in the case of myoglobin is 0, and since n = 1, = 1 mm Hg. For hemoglobin, the y intercept is -4.0. Using... 

Figure 7.6 Oxygen association with myoglobin (Mb) and human hemoglobin (Hb). (a) The Hill plot (b) a plot of oxygen partial pressure against the degree of hemoglobin saturation with oxygen.

Figure 8 Cooperative and noncooperative binding of O2. (a) Binding curves of myoglobin and hemoglobin, (b) Hill plot of binding curves. The Hill coefficient munber is determined from the first derivative (slope) of the HiU plots...

For hemoglobin, successive binding sites have different equilibrium constants and so the above equation has to be modified. It is found that the Hill plot for hemoglobin has a maximum slope of 2.8, giving a Hill coefficient of 2.8 (Fig. 6.8). A Hill coefficient greater than 1.0 indicates positive cooperativity. 

See also Hill Plots and Cooperativity, Models of Allosteric Activity, Oxygen Binding by Hemoglobin... 

Figure 7.9 Hill plots of oxygen binding for myoglobin and hemoglobin. 

This concept is similar to the conformational changes that occur in hemoglobin in response to changes in pH, fmctose bisphosphate (FBP), and other conditions. Kinetically, these effects can be described by Hill plots where log(vA max)/(l - vA max) is plotted versus log[S]. (See Chapter 6.) The magnitude of the slope gives the minimal number of independent binding sites. 

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