lecture 15 - 15-1MCB 354Lecture 15More about...

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Unformatted text preview: 15-1MCB 354Lecture 15More about ChymotrypsinLysozyme MechanismHexokinase Metal Ions in Enzyme CatalysisEnzyme Regulation: AllosteryLehninger, Chapter 6 :Enzymeskcat/KmChymotrypsin Exhibits a Bell Shaped pH-RateProfileHis57Ile16(-N-terminus)15-2Mechanism Based Inhibitors can Exploit the Nucleophilicity of Ser19515-315-4Phenylmethanesulfonyl fluoride: Inhibits serine proteases such astrypsin and chymotrypsin. Also inhibits cysteine proteases- with molecule that..i) binds to active site because it resembles a substrateii) forms stable covalent bond with group on enzyme close to active site- tosyl-L-phenylalanine chloromethyl ketone(TPCK)i) has L-Pheside chain, so binds to chymotrypsins active siteii) chloromethyl ketone group alkylates a ring N of His57iii) TPCK-derivative of chymotrypsin is enzymatically deadiv) D-Phe-isomer of TPCKineffectivev) TPCKreaction inhibited by a competitive inhibitorof chymotrypsinAffinity labeling of His57 in chymotrypsins active site(= example of a way of identifying in an enzymes active site)15-5Substrate specificity of serine proteasesis determined by binding pocket for R-group of the thatthe protease cleaves afterChymotrypsin:pocket (lined) withnon-polarbindsside chains of aromatic Trypsin:non-polar at base of pocketchanged to Asp, which can formion pair with +vely chargedside chains of Lys and Arg15-6Lysozyme Catalyzes Glycosidic C-O Cleavage 15-7Two Possible Mechanisms15-8DissociativeDouble DisplacementHigh energy carbocation vs. covalent intermediate15-9Glu35 acts as general base for hydrolysis of either carbocation or covalent intermediate 15-1015-11Which Mechanism is Operative?15-122-deoxy-2-fluoro sugarTrapped Intermediate Example of a reaction mechanismthat requires metal ions: enolaseGlycolytic enzyme that catalyzes reversible dehydration of2-phosphoglyceratetophosphoenolpyruvateAlso illustrates....general acid-base catalysistransition state stabilization15-13Enolase mechanism-1Another way Mg2+assists:Proton at C-2of 2-PG is normally not very acidic: not easily removed....
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lecture 15 - 15-1MCB 354Lecture 15More about...

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