Chymotrypsin is a digestive enzyme with a catalytic optimum between pH 7.8 and 8.0. However, due to the presence of gastric juice, chymotrypsin often functions in an environment of pH 5.5-7.0. The imidazole group of free histidine has a pK, of 6.0. Use the Henderson-Hasselbalch equation to determine the ratio of deprotonated to protonated His 57 imidazole moieties at pH 6.9. pH = pK₂ + log ( [His] [His+] 6.0 (VVI) Incorrect Aside from positioning, what do you think is the role of the Asp 102 residue? It allows nucleophilic attack by His 57. It raises the pK, of His 57. It protonates His 57 prior to substrate binding.

(a) A decapeptide has the following amino acid composition: Alaz, Arg, Cys, Glu, Gly, Leu, Lys, Phe, Val Partial hydrolysis yields the following tripeptides: Cys-Glu-Leu + Gly-Arg-Cys + Leu-Ala-Ala+ Lys-Val-Phe + Val-Phe-Gly. Reaction of the decapeptide with 2,4-dinitrofluorobenzene yields 2,4-dinitrophenylysine om the experimental data, deduce the primary structure of the decapeptide.

Identify and describe how you would PEGylate this peptide at its N- terminal amine. Discuss the reaction conditions you need to carry out the reaction and explain how pH affect selectivity of reaction. Draw the chemical structure of the resulting mPEG peptide conjugate.

Ornithine is an amino acid that is not used in the synthesis of proteins, but is an important intermediate in several metabloic pathways including the urea cycle and the synthesis of polyamines. It has a perfectly ordinary terminal amino group and terminal carboxyl group like any other amino acid and a side chain with a single ionizable side group with a pKa of 10.3. If ornithine is placed in solution at pH 7.0, it has a net charge of +1. What would the net charge on this amino acid be if the pH of the solution was raised to pH 12.0? Please explain your reasoning.