Table 1.

pK values for the ionizable groups in proteins from the literature

These pK values were measured at various temperatures, as noted below. Typically, the error in the measurements is ±0.1–0.2. In some studies no salt was present, and in some the ionic strength was not given. We have not corrected any of the values given in the original articles. Usually the errors in measuring the pK values are greater than these corrections (Tanford 1962).

^aDetermined using various model compounds at 25°C, as described in Table 1 in Chapter 20 of Cohn and Edsall (1943).

^bDetermined using various model compounds at 25°C, as described in Table 3 of Nozaki and Tanford (1967).

^cDetermined with Gly-Gly-X-Gly-Gly pentapeptides by ¹³C NMR at 26°C, except for Tyr, which was determined at 33°C (see Gurd et al. 1972^; Keim et al. 1973). Both termini of the peptides were not blocked.

^dDetermined in Gly-Gly-X-Ala tetrapeptides by ¹³C NMR at 35°C (see Richarz and Wuthrich 1978). Both termini of the peptides were not blocked.

^eFrom Creighton's textbook on protein biochemistry that references some of the values from the previous columns (Creighton 1993).