Lysine titration curve

Using the pKa values from problem 3, construct the theoretical titration curve showing the equivalents of H+ or OH reacting with 1 mol of glycine as a function of pH. Note that the shape of this curve is independent of the pfCa. Sketch similar curves for glutamic acid (pK./s equal 2.19,4.25, and 9.67), histidine (pfCa s equal 1.82,6.00, and 9.17) and lysine (pfCa s equal 2.18,8.95, and 10.53). 

The effects of mutating surface charge are mimicked by changes of pH. Below pH 5, the carboxylates become protonated, whereas above pH 9 the ammonium groups of lysine residues deprotonate, causing them to lose their positive charge. The changes in protonation state cause perturbations in the titration curves of the enzyme at extremes of pH. These effects are most marked at low... 

Titration curves of glutamic acid, lysine, and histidine. In each case, the pK of the R group is designated pKR. 

Titration curve of /3-lactoglobulin. At very low values of pH (<2) all ionizable groups are protonated. At a pH of about 7.2 (indicated by horizontal bar) 51 groups (mostly the glutamic and aspartic amino acids and some of the histidines) have lost their protons. At pH 12 most of the remaining ionizable groups (mostly lysine and arginine amino acids and some histidines) have lost their protons as well. 

How do the true titration curves of aspartic acid and lysine differ from that of glycine Explain your answer. 

Figure 1-9 Titration curve of lysine. For clarity, the vertical axis drawn to scale.

The anomalously steep titration curve (pH 4 to 6) of collagen in 0.5 M NaCl (Bowes and Kenten, 1948) raises the possibility of the existence of masked groups in this protein. Drifts in pH could not be detected because attainment of equilibrium with the solid phase requires 3 days. The steepness is quite marked compared to that of wool (Steinhardt, Fugitt, and Harris, 1940a) in the same pH range thus effects due to the existence of separate phases are probably not responsible. The fact that only part of the lysine appears to be titrated lends strong support to the hypothesis of acid-labile masking in this protein (see Section II, 5 of this paper). 

Additionally, Ti data for smaller oligomers of lysine have also been measured (Saito and Smith, 1974). Similarly, titration curves have been applied to the study of helix-coil transitions in aqueous solutions of poly-L-glutamic acid (Lyerla et al., 1973). 

Mathematical Sketch a titration curve for the amino acid lysine, and indicate the p values for all titratable groups. Also indicate the pH at which the amino acid has no net charge. 

Figure 4. Titration curves of glutamic acid, glycine, histidine, and lysine. The three amino acids whose titration curves sharply cut the zero-charge-horizontal-line also have a net charge apart from zero in the vicinity of the pH where they cut the zero line, i.e., the pi. That means that they have buffering capacity and conductance in the neighborhood of the isoelectric point and therefore are useful as carrier ampholytes. Glycine, on the other hand, with its extended horizontal part of the curve is not suitable. (Svensson, 2.)...

In this enzymatic reaction, the catalytic constant, ftcati is the rate-limiting step in the propan-2-ol —> acetone direction a plot of log fccat versus pH has a shape of a titration curve for a monobasic acid with pKa value of 7.0, suggesting that a histidine residue is involved in catalysis in the ternary complex enzyme-NAD" -alcohol (Maret Makinen, 1991). However, this assignment is not unambiguous, since carboxyl groups are known to have pK s as high as 8, and lysines to have pita s as low as 6. 

The following figure gives a proton titration curve of poly (L-lysine) in aqueous... 

Figure 1.14. Titration curve for lysine, pKai is for a-COOH. pKcafor a-NHl, and pKos pr...

Ehrenberg and Lewis (418) reported a titration-like pH dependence for the rate of formation of the unprotonated C=N stretching frequency (1619 cm-l) and for that of the M430 C=C frequency (1566 cm l). Similar observations were made by Kalisky et al. (419), who measured the pH dependence of the rate-constant ratio kx,ccq - M4i(/kL550 BRt at low temPeratures All curves show an inflection point around pH = 10, indicating that the rate of deprotonation of the Schiff base is controlled by a protein residue of pK = 10, such as tyrosine or a lysine, as proposed by Lewis et al. (235). On the basis of the same data... 

Horner (1954) constructed a theoretical curve for the titration of wool with alkali using amino acid analyses and the pKa values obtained for the side-chain groups of lysine, tyrosine, and arginine in the form of the free acids. He obtained a better fit using the Donnan expression of Peters and Speakman (1949) than he did with the Gilbert-Rideal (1944) expression. Obviously, much depends on the pKa values used hydrogen bonding in a protein structure can shift these values by more than one pH unit. Also, the assumption was made that the affinity of sodium ions for the... 

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