Handout2

Handout2 - Erin Yee ejyee@ucsd.edu BIBC 102 DI Thurs 5-6...

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Unformatted text preview: Erin Yee ejyee@ucsd.edu BIBC 102 DI Thurs 5-6 Handout 2 Chymotrypsin: (see mechanism on page 208-209 in text) A serine protease (enzyme that hydrolyzes peptide bonds) o All have serine in active site (R chain CH 2-OH) Cleaves bond on the C-terminus side of aromatic AAs Chymotrypsin side chains: o Asp 102 o His 57 o Ser 195 o Gly 193 Hydrophobic pocket: where the aromatic group on the AA resides during the reaction Key Steps to Know: o When the substrate binds to the active site, the Induced Fit compresses the hydrogen bond between His 57 and Asp 102 turning the side chain of His 57 into a strong base (its pka increases from 7 to 12) o This side chain of His 57 is then capable of deprotonating the hydroxyl group in the side chain of Ser 195 o When the proton of the hydroxyl is stripped away, the resulting oxyanion is a powerful nucleophile and can attack the carbonyl group of the substrate Michaelis-Menten Enzyme Kinetics: *Only consider the initial forward reaction Rates: o 1) Rate of product formed = k 2 [ES] o 2) Rate of ES dissociation back to E + S: k -1 [ES] o 3) Rate of E + S ES: k 1 ([E T ]-[ES])[S] Steady-State Assumption: o Rate of ES formation = Rate of ES breakdown (Rate 3 = Rate1 + Rate2) Simplifying the Steady-State assumption, you get the Michaelis-Menten Eqn: o Vo = V max [S] K M + [S] And also the Michael-Menten Constant: o K M = k 2 + k -1 units: M k 1 o This constant indicates how good a substrate is for a particular enzyme or in other...
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This note was uploaded on 02/20/2010 for the course BIBC 102 taught by Professor Price during the Spring '02 term at UCSD.

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Handout2 - Erin Yee ejyee@ucsd.edu BIBC 102 DI Thurs 5-6...

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