Grimsley GR, Scholtz JM & Pace CN, 2009
Grimsley, Scholtz, and Pace report a nearly complete set of mean pK values culled from 541 pK values measured in 78 folded proteins in their 2009 paper (1). The vast majority of measurements were made directly using nuclear magnetic resonance. A small number of pK measurements were made by indirect methods.
Amino acid pK values from Grimsley GR, Scholtz JM & Pace CN, 2009 (1).