5-Enzyme mechamism handout2

Kinetics catalysis enzyme catalysis 2 rnase example 1

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Unformatted text preview: an the reactant and/or the products, are more thermodynamically stable than transition states. ifmorestablethan product,product wouldn'tform? Intermediateinrxn-->isitduetopresenceofenzyme?couldsuchintermediatebeformed withoutenzyme?? RNase: acid/base catalysis 5. Base forms a strong nucleophile (HO-) nowREPROTONATED waterpositionedclosetobase whyistherewaternow,nowaterbefore?? OnehalfofactivesiteisOPEN,waterflushesin Transition state #2 RNase: acid/base catalysis 5. Base forms a strong nucleophile (HO-) Water enters the active site on departure of Product 1 His-119 now acts as base and deprotonates water, creating a stronger nucleophile. The resulting hydroxide ion (stronger nucleophile) attacks the P-atom to form a new P-O bond – and the second transition state. RNase: acid/base catalysis 6. Acid forms a better leaving group (ROH) RNase: acid/base catalysis 6. Acid forms a better leaving group (ROH) His-12, acting as an acid, donates a proton to the...
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