Thurlkill RL, Grimsley GR, Scholtz JM & Pace CN, 2006

Thurlkill, Grimsley, Scholtz, and Pace report a nearly complete set of pK values measure by potentiometric titration of alanine pentpeptides in their 2006 paper (1). The peptide model used in this study was Ac-AAXAA-NH2 and pK values were measured at 25 oC in 0.1 M KCl.

Amino acid pK values from Thurlkill RL, Grimsley GR, Scholtz JM & Pace CN 2006 (1).

Group

3.67

†‡

ASP

3.90

†¶

GLU

4.25

†§

HIS

6.54

†€

8.00

†¥

CYS

8.55

†*

TYR

9.84

†•

LYS

10.40

†£

ARG

12.3

†¤

† Data from Table 2.

‡ The reported value is 3.67 ± 0.03.

¶ The reported value in Table 2 of this paper is 3.67 ± 0.04. This value is corrected to 3.90 ± 0.02 in another paper by the authors (2). The reason given for the correction of the value is "further measurments under the same conditions on a newly synthesized peptide."

§ The reported value is 4.25 ± 0.05.

€ The reported value is 6.54 ± 0.04.

¥ The reported value is 8.00 ± 0.03.

* The reported value is 8.55 ± 0.03.

• The reported value is 9.84 ± 0.11.

£ The reported value is 10.40 ± 0.08.

¤ Due to the high pK value of the guanidino group of arginine, no measured value is reported. The authors used the value of 12.3 in a later review paper (3). This value is the pK value of the guanidino group in the free amino acid arginine from Cohen & Edsall (1943) corrected for the influence of the negative charge on the carboxylic acid (4).