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-   -   How to find net charge of this peptide at pH 9? (http://www.molecularstation.com/forum/biochemistry-forum/86612-how-find-net-charge-peptide-ph-9-a.html)

 Doctor 10-10-2012 04:19 PM

How to find net charge of this peptide at pH 9?

The peptide is as follows:
"TIMELYRAIDINGPARTY"

The right answer to this question is net charge of -1, but I have no idea how they got this answer.
:frusty:

 Kunal Pandya 10-11-2012 04:08 AM

Re: How to find net charge of this peptide at pH 9?

Sequence is NH2-Thr-Ile-Met-Glu-Leu-Tyr-Arg-Ala-Ile-Asp-Ile-Asn-Gly-Pro-Ala-Arg-Thr-Tyr-COOH

Among above sequence Thr,Ile,Met,Leu,Ala,Asn,Gly,Pro not having any charge at any pH because of their side chain (i.e. this amino acid give charge only if they have a N terminal or Carboxyl terminal position in peptide)

Glu,Asp having No charge (Approx) below pH 4 (as pKa 4) and above pH 4 each contribute -1 charge

Arg,Lys,His having +1 charge below their pKa value and If pH is above their pKa value they having 0 Charge (i.e. No charge)

Cys ,tyr having Zero charge below their pKa value while contribute -1 charge at pH above their pKa value.

N terminal amino of Thr having pKa value 9.1 so it upmost uncharge and contribute Zero Charge to Peptide, While COOh of tyrosine having -1 Charge at pH 9 So

(0) Amino of Thr + (-1) Glu + (-1) Asp + (+1) Arg + (+1) Arg + (-1) Tyr = -1 Net Charge

For pKa Value of amino acid go through this link