logo.gif (3296 bytes)Introduction to Protein Structure

Overall Charge on a Peptide -- Example 2


Serylaspartylvalinylglutaminyllysine
(Ser-Asp-Val-Glu-Lys; SEVQK)

Note: ionizable groups are "boxed"

wpe21.jpg (10731 bytes)

 

In addition to the amino group (pKa ~ 9) and the carboxyl group (pKa ~ 3) at each end of the molecule, the sidechains of the aspartic acid (carboxyl group; pKa ~ 4.4) and the lysine (amino group; pKa ~ 10) residues are ionizable.

Thus, the net charge on this peptide at three different  pH's ( 2, 7 and 11) is as follows:

Charge on Functional Group
pH N-terminus Asp -COOH Lys -NH2 C-terminus Net Charge
2.0 1+ 0 1+ 0 2+
7.0 1+ 1- 1+ 1-
11.0 1- 0 1- 2-

Copyright 1998, 1999, 2007 by Frank R. Gorga;   Page maintained by F.R. Gorga;   Last updated: 12-Mar-2007