Chemistry > SOLUTIONS MANUAL > San Jose State UniversityCHEM 135F12 135, MT 3 Solutions (All)

San Jose State UniversityCHEM 135F12 135, MT 3 Solutions

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Name ID # Chem 135 Midterm 3 Fall 2012 1. (15 points) Papain (from papayas) catalyzes the hydrolysis of peptide bonds and belongs to the family of proteins known as the cysteine proteases. The ess ... ential residues at the active site of the enzyme are a protonated His and an unprotonated Cys. The enzyme has a bellshaped pH-rate profile with the midpoint of the rising leg at a pH of 4.2 and the midpoint of the falling leg at a pH of 8.2. Based on the fact that a thioester intermediate forms along the reaction pathway, draw the reaction mechanism of papain catalyzed peptide bond hydrolysis, depict a reaction coordinate diagram consistent with this mechanism, and assign pKa values to the essential residues. Solution: N NH E H R N O R' H E S R NH O S R' E N NH E H R S O E H O H R'NH2 N NH E R S O O H E N NH E H RCO2H E S + N NH E H The cysteine residue has pKa a value of 4.2 (since it is unprotonated at the beginning of catalysis) while the histidine has a pKa value of 8.2. ΔG Reaction Coordinate 2. a) (9 points) Draw the structure of the glycerophosphplipid phosphatidyl choline, in which a 14:0 fatty acid is esterified to the sn1 position and a 12-hydroxylated version of an 18:1 ω9 fatty acid is esterified to the sn2 position. Solution: O O O OH O O P O O O N(CH3)3 [Show More]

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