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Titration Curves: Titration of Tyrosine

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1) Plot the pH titration of tyrosine, whose structure is shown attached at pH = 7.0. Show:
a) The pH value at each equivalence points and each 1/2 equivalence point
b) The charge at each equivalence and 1/2 equivalence point
c) The isoelectric point of the amino acid and give its value
d) The approximate shape of the titration curve

2) Draw the structure of tyrosine at pH = 9.59.

Look at the diagrams in the document.

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Solution Summary

The pH titration of tyrosine is plotted and its structure is drawn.

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1. If the active site of a dipeptidase contains a glutamic acid residue (pKa 3.3) and a histidine residue (pKa 6.7), both of which must be charged for the substrate to bind, what is the optimal pH for substrate binding?

2. Lysozyme catalyzes the hydrolysis of C-O-C bonds between sugar residues in bacterial cell walls. The proposed catalytic mechanism for lysozyme requires that the side-chain group of aspartic acid-52 be in the ionized -COO- form and that of glutamic acid-35 be in the un-ionized -COOH form.

(a) What percentages of Asp and Glu side-chain groups would be in the ionized -COO- form at pH 5.0, the pH optimum for the hydrolysis of chitin by lysozyme, assuming pKas for the side-chains as given in Table 4.1 (attached) of Garrett and Grisham?

(b) In view of your answer to part (a), explain how it is possible for Glu-35 in lysozyme to be present in the un-ionized form.

3. A solution which contains a mixture of three tripeptides -- 1) Tyr-Arg-Ser, 2) Glu-Cys-Phe, and 3) Asp-Asp-His -- is chromatographed on CM-cellulose at three different pHs: 6.0 8.0, and 10.0. In what order will each of the peptides emerge from the column at each of these pHs? Use Table 4.1 in the Garrett and Grisham text for amino acid pKas. The pKa for the CM-cellulose is 4.90.

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