Given the following peptide
SEPIMAPVEYPK
a. Estimate the net charge at pH 7 and at pH 12. Assume the pKa values given in Table 5.1.
In Table 5.1

b. How many peptides would result if this peptide were treated with (1) cyanogen bromide, or (2) trypsin, or (3) chymotrypsin?
c. Suggest a method for separating the peptides produced by chymotrypsin treatment.

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TABLE 5.1 Name Properties of the common amino acids found in proteins pKa of lonizing Residue Mass Occurrence Side Chain Abbreviations 1- and 3-letter codes aCOOH Group A, Ala R, Arg N, Asn pKa of pKa of -NH3 Group (daltons) in Proteins (mol %) 9.7 Alanine Arginine Asparagine Aspartic acid D, Asp Cysteine Glutamine Glutamic acid E, Glu Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine F, Phe Proline Serine Threonine Tryptophan yrosine Valine 71.08 156.20 114.11 115.09 103.14 128.14 129.12 57.06 137.15 113.17 113.17 128.18 131.21 147.18 97.12 87.08 101.11 186.21 163.18 99.14 2.3 2.2 12.5 8.8 9.8 10.8 5.0 4.2 5.9 1.3 3.7 3.9 8.3 C, Cys O, Gln 2.2 2.2 2.3 9.7 9.6 9.2 9.7 9.6 9.0 9.2 4.2 G, Gly 7.9 2.4 5.5 IS 2.4 L, Leu K, Lys M, Met 2.2 10.0 2.0 4.0 P Pro S, Ser T, Thr W, Trp Y, Tyr V Val 10.6 9.2 10.4 9.4 5.6 2.4 1.5 10.1