Intrinsic pKa

The intrinsic pKa thus represents the pK of the group in the protein with all other titratable amino acids in their neutral state. Finally, the interaction energy, between the sites i and j, is... 

Del Buono GS, Figueirido FE, Levy RM (1994) Intrinsic pKas of ionizable residues in proteins An explicit solvent calculation for lysozyme. Proteins 20 85-97. 

Figure 3-2 Acid-base titration curve for hen lysozyme at 0.1 ionic strength and 25°C. O, initial titration from the pH attained after dialysis , hack titration after exposure to pH 1.8 A, hack titration after exposure to pH 11.1. The solid curve was constructed on the basis of "intrinsic" pKa values based on NMR data. From Kuramitsu and Hamaguchi5...

Knowles JR (1976) The intrinsic pKa-values of functional groups in enzymes improper deductions from the pH-dependence of steady-state parameters. CRC Crit Rev Biochem 4 165-173... 

The intrinsic pKas of the proteins depend on the local environment. They are further influenced by ionic strength, dielectric constant, and temperature. Mobility estimates should account for the effective mass-to-charge ratio and molecular shape contributions. The denaturation processes produce sets of... 

Quartz is a crystalline form of SiC>2 where silicon is tetrahedrally bound to four oxygen atoms. At the surface of quartz and other siliceous substances, acidic silanol groups formed from hydrolysis are present. Surface silanols are titratable in aqueous solution and are a source of pH-dependent surface charge. Fully hydroxylated silicas are considered to have a silanol population of 5/nm2 with an intrinsic pKa from 5.8 to 7.2 [18]. 

The result of this charging effect on inhibiting dissociation is that the apparent pAa of polyprotic organic acids can only be compared directly with the pA, of monoprotic organic acids when the polyprotic acid is undissociated (a = 0). Thus, the pKa value at a = 0 is called the intrinsic pKa of the humic material. The relationship of the apparent pA to the intrinsic pKa is given by... 

FIGURE 2.9 Dissociation of acids as function of pH. (a) Calculated degree of dissociation (a) of a fatty acid (intrinsic pKa — 4.7) at very small ionic strength, (b) Titration curves, i.e., experimentally determined degree of neutralization (a ) by KOH of citric acid and phosphoric acid the intrinsic pK i values are indicated by vertical dashes. 

Effect of Surface Charge and Surface Dielectric Constant on pK The apparent pKa of a dissociable group at the biosurface differs from the intrinsic pKa of the group in bulk solution, due to the electrostatic enhancement of the hydrogen ion concentration (activity) at the interface, caused by the surface charge, and also due to the shift in the acid-base equilibrium arising from the different local polarity at the interface. ... 

In the discussion above we considered only a single titratable site. To extend the procedure to multiple sites first requires that the pKa be calculated for each site according to Eqs. [410]-[412]. The pK of a site determined while all other sites are unprotonated is called the intrinsic pKa of the site. We now define a protonation vector x = x, X2, , xn for N sites where each x l is either 1 or 0 depending on whether the site is protonated x thus spans a space of 2N vectors and x denotes one of them. The charge on site p corresponding to state n is then... 

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