Table I Theoretical molarity of functional groups in a complete digest of 100 μg of a human proteome. Estimations are based on average peptide length, and pKa values were taken from literature (22, 27)
Functional groupAmount in nmol (100 μg peptides)pKa
α-amine on N-term787.7 ± 0.5
ε-amine on Lys3810.5 ± 1.1
Primary amines116
Hydroxyl on Tyr2510.3 ± 1.2
Hydroxyl on Ser76∼16
Hydroxyl on Thr49∼16
Hydroxyl groups150
Imidazole on His246.6 ± 1.0