# Homework Help: How to calculate the pI of a peptide?

1. Oct 10, 2006

### DDS

How to calculate the pI of a peptide??

Hello everyone, I am hoping someone can shed some light on this question. I know the general idea behind it but i cant seem to put the nail in the coffin.

The sequence is ATLDAK and it asks to : Calculate its approximate pI

This is what i have so far:

........nT-A......T.....L..... D.... A.... K-...... cT
pK...9.87.......................3.9........10.54...2.16

I know that there are 2 positive charges so this results in requiring to be deprotinated with two equivalents of base. I also know that the pI is given by the two amino acids that give the zwiterionic charge, or simply zero charge. However, how to identify those amino acids....????