Cohen EJ & Edsall JT, 1943

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Cohen & Edsall provide a nearly complete set of pK values for the free amino acids in their classic text, Proteins, amino acids and peptides as ions and dipolar ions (1943) (1). The pK values are for the free amino acids in solution at 25 oC and are taken from the original publications reporting these values for the amino acids through the 1920s and 1930s.

Amino acid pK values from Cohen EJ & Edsall JT, 1943 (1).

Group

2.14

†‡

ASP

3.65

†

GLU

4.25

†

HIS

6.00

†

9.47

†¶

CYS

8.33

†§

TYR

10.07

†

LYS

10.53

†

ARG

12.48

†

† Data from Table 5.

‡ This value is derived from these data by determining the mean value of the α-carboxylic acid pK values for the nineteen amino acids listed in Table 5 (THR is ommitted).

¶ This value is derived from these data by determining the mean value of the α-amino group pK values for the nineteen amino acids listed in Table 5 (THR is ommitted).

§ Note that the pK values of the α-amino group (10.78) and the sulfhydryl group (8.33) are misrepresented in Table 5. These pK values are incorrectly reversed in Table 5.

References

(1) Cohen EJ, Edsall JT (1943) Proteins, amino acids and peptides as ions and dipolar ions, Reinhold, New York