[jessica]

hi guys,  i have an exam coming up in 2 weeks but i am still confused as to how to find the pI value for a polypeptide.

calculate the pI for dodecapeptide TALKINGHEADS assuming solution values for the amino acid side chain pkas, a value for the pka of the amino terminus, and using the information that the C-terminal carboxyl group of the peptide exists as the methyl ester.  In what direction will this peptide migrate in an electric field if the pH of the medium is 7.0?

and here is what i have so far

H2N-T..A..L..K..I..N..G..H..E..A..D..S-CO2H
....10.54...6.04..4.07..3.90

and i am clueless to what the next step to solve the problem should be.  please help =)

[chiralic]

Dear Jessica:

Started with these links:

1) http://www.bio.mtu.edu/campbell/pkprob1.html

2) http://www.innovagen.se/custom-peptide-synthesis/peptide-property-calculator/peptide-property-calculator-notes.asp

3) EMBL WWW Gateway to Isoelectric Point Service
    http://www.embl-heidelberg.de/cgi/pi-wrapper.pl

4)Expert Protein Analysis System < http://ca.expasy.org/>
   Check it out on : http://ca.expasy.org/tools/pi_tool.html

Good luck!

Chiralic