MCB 450 1st Edition Lecture 11 Outline of Last Lecture I Principles of Enzyme Catalysis a Free Energy and Equilibria b Keq and G in Living Cells c Activation Energy d Enzyme Substrate Interaction Outline of Current Lecture I Effect of substrate and enzyme on reaction rate II Km and Vmax III Kcat IV kcat Km V Bi substrate reactions Current Lecture Big Picture S substrate P product E enzyme 11 18 Small Km low S Large Km high S Determination of Km and Vmax from double reciprocal plot Know this for exam questions 11 22 Illustrates the different enzymes and whether they have large or small K m s Generalization about Km Km of an enzyme for its substrate is often near the concentration of that substrate in the cell Kcat rate constant for the rate limiting step in an enzyme catalyzed reaction Km s and Kcat s can vary drastically between enzymes Problem Expect higher impact on activity If total amout of E is increased Vmax will increase because Vmax k 2 E1 or kcat E1 But km k1 k2 which is independent of E so will km be the same or different o Km will be the same B is the correct graph 11 29 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Can use kcat and km to compare enzymes 11 30 Chymotrypsin prefers bulkier substrates like phenylalanine The different values of kcat km tells us which is the better substrate for chymostrypsin o The higher the number the better When kcat Km tells us about an enzyme If enzyme binds the substrate too well then you can make the reaction rate lower and increase the activation energy Know slide at end of lecture that has all of the different forms of these equations Solving kcat and kcat Km problems Given Vmax 75 umoles 3 min 25 umoles min 1 Et 10 10 2g 5x10 4 g mol 1 2 x 10 7 moles Kcat Vmax Et 2 5 x 10 5 moles min 1 2 x10 7 moles 1 25 x 10 2 moles min o The sort of calculations we might get on the exam Ping pong reaction covalently modified enzyme intermediate Chymotrypsin can be categorized as a ping pong reaction
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