Notes on...

Calculating the net charge

The net charge Z of a peptide at a certain pH can be estimated by calculating

The equation for the net charge of a peptide.

where Ni are the number, and pKai the pKa values, of the N-terminus and the side chains of Arginine, Lysine, and Histidine. The j-index pertain to the C-terminus and the Aspartic Acid, Glutamic Acid, Cysteine, Tyrosine amino acids.

Innovagen's Peptide Property Calculator calculates the net charge for all pH values of 0.1 to 14 in increments of 0.1, and plots these producing a titration curve.

This algorithm has its limitations, some of which are:

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