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  Home > JCE Print > Journal of Chemical Education > Issues > 2002  > August  >
In the Classroom
A Graphical Approach to Determine the Isoelectric Point and Charge of Small Peptides from pH 0 to 14
Gabriele D'Andrea and Giuseppe Di Nicolantonio
Department of Biomedical Sciences and Technologies, University of L'Aquila, Coppito 2, I-67100 L'Aquila, Italy
Cover
August 2002
Vol. 79 No. 8
p. 972
Abstract
The knowledge of a peptide's isoelectric point (pI ) value and its charge value from pH 0 to 14 is of great importance in biology and medicine. Many separation and purification techniques and medical applications depend on the knowledge of these two values. However, students often find it difficult to determine the pI in small peptides with three or more ionizable groups. A graphical approach is here reported with a general linear equation and helpful reminders and rules. Examples of the method are given to determine the pI value in relatively simple peptides and their charge in the pH range from 0 to 14. In applying the general as well as the correlated equations, researchers, students, and teachers should be aware that the actual pK values of ionizable groups in peptides could be quite different from the ones known for the single amino acids from which they are produced. A program list in Pascal is also provided to determine the peptide pI value and its charge in the pH range 0 to 14.
Supplement
A program list written in Pascal by which it is possible to determine the peptide pI and its charge in the pH range 0 to 14, once the main peptide parameters are inserted, is available. As an arithmetic exercise the program can accept up to 20 pK values. All equations included in the program are based upon a graph of q versus pK.
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*  Citation
 D'Andrea, Gabriele; Di Nicolantonio, Giuseppe. J. Chem. Educ. 2002 79 972.
*  Keywords
 Amino Acids; Biochemistry; Teaching / Learning Aids
*  History
 Created:
Last Updated:		 July 23, 2002
March 16, 2005
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