Number of hydrogen ions bound

The numbers of hydrogen ions bound that are calculated using this equation are based on the arbitrary convention of not counting the additional 12 hydrogen atoms in ATP. Thus, the average number Nvt of hydrogen ions bound by ATP is given by... 

Figure 7.7 Plot of the average number of hydrogen ions bound by the unoccupied catatytic site of fumarase at 25°C and an ionic strength of 0.10 M. [With permission from R. A. Alberty, J. Phys. Chem. B 104, 9929-9934 (2000). Copyright 2000 American Chemical Society.]...

The binding capacity for the unoccupied site, which is calculated using equation 7.6-11, is plotted versus pH in Fig. 7.8. The number of hydrogen ions bound by the catalytic site in the fumarase-L -tartrate complex is plotted in Fig. 7.9. This is steeper than the titration curve of a diprotic acid with identical and independent groups. The binding capacity for the site occupied by meso-tartrate is shown in Fig. 7.10. The slope of the binding curve is steeper than for the unoccupied site shown in Fig. 7.6, as expected since the binding is cooperative. 

The procedure described in the preceding paragraph will of course measure the number of hydrogen ions bound to or dissociated from all substances which are present in the solution under study. The accuracy of an experimental electrometric titration curve depends to a considerable degree on the absence of buffers, carbon dioxide, and any other substance, other than the protein of interest, which is capable of acting as an acid or base. 

Electrometric titration is simply a measure of the total number of hydrogen ions bound to or dissociated from a protein molecule, with no discrimination between the various kinds of acidic or basic groups with which these hydrogen ions may be associated. Thus there is a need for alternative methods which focus specifically on hydrogen ions associated with partic-lar groups of the protein molecule. 

Throughout this paper we have so far discussed only the average number of hydrogen ions bound to or dissociated from a protein molecule at any pH. It should be pointed out that individual protein molecules may at any given instant have Zh values which can be larger or smaller than the average value Zu Edsall (1943) has shown for example that in hemoglobin at pH 6.4, where — 0, 4% of all molecules have Zs = -f3, 9% have Zh = -f2, 17% have Z = +1, 22% have Z = 0, 21 % have... 

The average number of hydrogen ions bound by ATP beyond those bound at pH 9 is given as a function of pH by Nh=T2+ 2ri. 

The average numbers of hydrogen ions bound by inorganic phosphate at ionic strength 0.25 M and pHs 5, 6, 7, 8, and 9 is given by... 

The rate of change of the standard transformed entropy of formation with pH can be calculated in two ways (1) directly and (2) from the rate of change of the temperature times the average number of hydrogen ions bound with temperature, as shown in equation 3.4-13. 

The same table of standard transformed entropy of formation of inorganic phosphate can be calculated from the average number of hydrogen ions bound using... 

There are two ways to represent the titration curve for a protein or other polyprotic weak acid. The usual thermodynamic way used in Chapter 2 is to represent the average number of hydrogen ions bound with... 

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