BU BI 421 - Lesson 6 Enzyme Kinetics

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kinetics study of the rate of reactant compounds Rate of enzymatic reaction Is affected by Enzyme Substrate Effectors and Temperature Ki E SEES K Reasons for studying Quantitative description of biocatalysts Determines Order of binding of substrates Elucidate acid base catalysis Understand catalytic mechanism find effective inhibitors and understand regulation of activity Maximum Velocity Vmax T tl max cid 15482 I i km i km STCMM s cmM S substrate concentration Vmax maximum velocity vo im ia velocity Km Michaels constant step I Rate of formation and breakdown of ES governed by rate constants K I Es 114 ES K F ES S step Rate of formation and breakdown s equal steady state ASSUMPTION K E ES 57 14 ES 1142 ES Enzyme substrate complex y Mita s enzyme 1substrate Tv COBB 1929m Gaggi j a enzyme product gress substrate Site En g C Act e N Enzyme E combines with its substrate to form an enzyme substrate ES complex in a fast reversible step ES complex then breaks down na slower second step 10 yield the free enzyme and the reaction product CP Effect Of Substrate Concentration On Reaction Rate Es cid 15482 EtP Kz kz A Time Michaelis Menten Equation B c 1m Substrate concentration E CS mM E km SJCMM Rate limiting step in enzymatic reactions Is the breakdown of ES complex 10 product and free enzyme Early reaction concentration of product is negligible simplifying assumption made p 7s can be ignored Reaction reduces 10 K KI turnover show many substrate molecules one enzyme molecule can convert per second C SEES E P Step 3 Algebraically solve for ES and define Micheal s constant kmas Kitkz ki K K E 5 k ESTES K 114 ES K E S K 1K ES s 1K as Y im Y s E5 ia L cess I E a step 4 Express llointermsof ES and simplify Eg 0 142 Es 2 E S cid 15483 Yma Kz Et yo Vma Kinetic Parameters Nonlinear Michaelis Menten plot calculates km Vmax Max velocity Vmax I 1 K M SJLMM Enzyme Efficiency Limited by speolfity Kca K ms Kca Kz Diffusion from active site limits maximum value for specificity Gain efficiency by having high velocity affinity for substrate catalase us acetylcholinesterase Enzymes Keat Km close 10 Diffusion controlled Limit Clio 1010 M s 5 Enzyme substrate Kcatcs Acetylcholinesterase Acetylcholine Carbonic anhydrase coz Hoo 1 1202 Crotonyl CoA Fumarate Malate Benzylpenicillin 1 4 104 1 106 4 105 4 10 5 7 103 8 102 9 102 2 0 103 Catalase Crotonase Mara B Lactamase kmcs 1 9 10 5 1 2 10 2 2 6 10 2 1 1 100 2 10 5 5 10 6 2 5 10 5 2 10 5 kcatlkm M 151 1 6 108 8 3 107 1 5 107 4 10 2 8 108 1 6 108 3 6 107 1 108 to determined by breakdown of Esto form product determined by ES Vo kz ES Not easily measured alternative expression Et Represents the total enzyme concentration sum of free and substrate bound enzyme introduced Free Unbound enzyme E Et ES 5 Is Et amount of substrate bound by the enzyme is negligible compared to the total S Vous s approaches Vmax at high s cannot accurately determine Vmax km from nonlinear graphs Derived by the reciprocal of both sides I V0 Km Vmax S 11 Vmax I Vous l S straight line Y Intercept 71 11 Max Intercept 3 11km

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