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Homework Help: Calculating the theoretical net charge

  1. May 13, 2007 #1
    I was given this peptide:


    I then amidated the C-terminal, and i need to figure out how to calculate the theoretical net charge of the amidated peptide.
    Can anyone help me please!!
    I have a feeling it is something to do with the isoelectric point but i'm not sure.
  2. jcsd
  3. May 14, 2007 #2


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    Since you have capped the carboxyl terminus (the amine terminus remains), this question is asking you to determine the charges of the side groups of the peptide. Write down all of the peptides that have ionizable side groups and their pKa's. Determine which ones will be protonated and deprotonated at the pH (which is not given by you in your OP). Ignore ion pairs and count the excess negative or excess positive charges. Don't ignore the amine terminus' pKa (as ammonium ion).
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