Peptide ionization Consider a peptide with the sequence Ser-His-Glu-Cys-Arg-Gln. You will be asked to state the charge on the functional groups of this peptide at pH 1 and pH 9.5. You will also be asked to calculate the net charge on the peptide. You may find it convenient to write down the charge on each group on a piece of paper as you go along, so that you can add them up at the end.
Peptide ionization Consider a peptide with the sequence Ser-His-Glu-Cys-Arg-Gln. You will be asked to state the charge on the functional groups of this peptide at pH 1 and pH 9.5. You will also be asked to calculate the net charge on the peptide. You may find it convenient to write down the charge on each group on a piece of paper as you go along, so that you can add them up at the end.
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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Question
I’m having trouble finding what His is can you please help?
Transcribed Image Text:At pH 1, the charge on the side chain of His is
-1
+1
0.
Transcribed Image Text:Peptide lonization
Consider a peptide with the sequence Ser-His-Glu-Cys-Arg-Gln.
You will be asked to state the charge on the functional groups of this
peptide at pH 1 and pH 9.5.
You will also be asked to calculate the net charge on the peptide. You may
find it convenient to write down the charge on each group on a piece of
paper as you go along, so that you can add them up at the end.
Assume the following generic pK, values for ionizable functional groups:
a-carboxyl:
side-chain carboxyl:
imidazole:
3.1
4.1
6.0
a-amino:
8.0
thiol:
8.3
E-amino:
10.8
aromatic hydroxyl:
guanidino:
10.9
12.5
Expert Solution
Concept.
The pKa of an amino acid that resides within a protein refers to the pKa of the side chain of that amino acid and this contributes to the net charge of the peptide. The charge on the alpha- amino and the alpha carboxyl, at the amino and the carboxyl terminus respectively, also determine the net charge depending on the pH of the buffer in which the petide is dissolved.
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