Chemical Education Today
Spreadsheet Enhancement to Calculating the pI of Proteins I enjoyed Paul Sims's recent article regarding the use of a spreadsheet to calculate net charges of peptides and proteins (1). From my experience, students respond well to using computers in the classroom. This spreadsheet was immediately incorporated into the curriculum for my undergraduate biochemistry class. Providing students with an opportunity to construct their own titration curves of amino acids, peptides, and proteins and learn the theory of why they receive a particular set of results enhances the students' understanding. Students can then easily understand the importance of determining the pI of a protein. I would also like to propose a powerful addition to the spreadsheet that Sims has developed. Spreadsheets have the capability of counting letters in addition to counting numbers. One can use the spreadsheet to count the number of each amino acid present in a particular sequence. First, copy a protein or peptide sequence in FASTA format into one cell in the spreadsheet. Next, in a second cell, type the following code, referencing the cell of your sequence: =(LEN(cell reference for sequence)-LEN(SUBSTITUTE(cell reference for sequence, amino acid letter to be counted,""))). This cell will then return a value that corresponds to the number of times a given amino acid appears in the sequence. Finally, repeat the calculation for each amino acid desired. This extra calculation in the spreadsheet is only meant to keep the students from obtaining counting errors for the number of times a given amino acid appears in a given sequence. The spreadsheet now has all of the capabilities of a “canned” program, but remains fully transparent and editable.
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Journal of Chemical Education
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Literature Cited 1. Sims, P. A. J. Chem. Educ. 2010, 87, 803–808. Richard H. Singiser Department of Chemistry, Clayton State University, Morrow, Georgia 30260, United States
[email protected] DOI: 10.1021/ed1009305 Published on Web 11/30/2010
Reply to “Spreadsheet Enhancement to Calculating the pI of Proteins” I welcome and appreciate the “spreadsheet enhancement” suggested by Richard Singiser (1). This enhancement greatly improves the functionality of the spreadsheet method of estimating isoelectric points (2), and I have implemented this change in our undergraduate biochemical methods course. Literature Cited 1. Singiser, R. H. J. Chem. Educ. 2011, 88; DOI: 10.1021/ed1009305. 2. Sims, P. A. J. Chem. Educ. 2010, 87, 803-808; DOI: 10.1021/ed100232j. Paul A. Sims Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States
[email protected] DOI: 10.1021/ed1010129 Published on Web 12/01/2010
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Vol. 88 No. 2 February 2011 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed1010129 Published on Web 12/01/2010
