BMS100_BCH_1.08-F22_ Enzymes II_Pre-learning slides.pptx
Transcript
Enzyme Kinetics Prelearning Part 1 Dr. Heisel BMS100 Michaelis-Menten Kinetics Michaelis and Menten (M & M) developed a kinetics equation for certain reactions* What do we use it for? To determine if an enzyme is physiologically useful based on its: Maximum rate Affinity for substrate (or inhibi...
Enzyme Kinetics Prelearning Part 1 Dr. Heisel BMS100 Michaelis-Menten Kinetics Michaelis and Menten (M & M) developed a kinetics equation for certain reactions* What do we use it for? To determine if an enzyme is physiologically useful based on its: Maximum rate Affinity for substrate (or inhibitor or coenzyme…) * What reactions can M & M kinetics be applied to? Michaelis-Menten Kinetics: Reactions M & M kinetics applies to first order reactions 1st order: Concentration of a single substrate is directly proportional to the rate of the reaction Not a continuation of the straight line: What is happening here? Hold that thought… Straight line: [S] is proportional to rate https://commons.wikimedia.org/wiki/File:MMkinetics.png Michaelis-Menten Kinetics: Reactions Many physiological reactions involve more than a single substrate So how do M & M kinetics apply? First order with two substrates = Enzyme that uses two substrates, A and B A B B B B B B • Consider what would happen to the rate if more A was added. What about if more B were added? • In each case, would the rate: • Stay the same, increase, decrease: why? • This type of reaction is called a “pseudo” first order reaction, and M & M kinetics still apply Michaelis-Menten Kinetics: Reactions Examples: What types of reactions are depicted? Which substrate is “ignored” in terms of M & M kinetics? Fumarate Malate +H2O Acetylcholi ne Acetate Choline +H2O https://commons.wikimedia.org/wiki/File:Malate_Dehydrogenase_Catalyzed_Reaction_of_LMalate_to_Oxaloacetate.jpg https://commons.wikimedia.org/wiki/File:Acetylcholine_metabolisme.png Michaelis-Menten Kinetics: Why do you Back to thethink graph the rate stops increasing as the [S] continues to increase? Not a continuati Zero on of the order straight line Straight line: [S] is First order proportional to rate End of Prelearning Part 1 Please review Part 2 Enzyme Kinetics Prelearning Part 2 Dr. Heisel BMS100 Michaelis-Menten Kinetics: Equation Vo = Vmax[S] / ([S]+KM) Initial velocity Maximum velocity Measure of enzyme affinity Vo: the initial rate of the reaction [S] is high and [P] is low, therefore no reverse reaction takes place Km: indication of how well the enzymes binds a given molecule Small Km = high affinity; large Km = low affinity Michaelis-Menten Kinetics: Graph Graphing [S] against reaction rate determines: Vmax (maximum rate) Km (enzyme affinity) https://commons.wikimedia.org/wiki/ Michaelis-Menten Kinetics: Graph Lineweaver-Burk = reciprocal of M & M equation Creates a straight line graph, easier to extrapolate Y-intercept = 1/Vmax Extrapolated X-intercept = - 1/Km 1 / Vo = (1 / Vmax) + (KM / Vmax) (1 / [S]) Y-axis Yintercep t Slop e X-axis 1 / Vo = (1 / Vmax) + (KM / Vmax) (1 / [S]) Y-axis Yintercep t Slop e X-axis https://commons.wikimedia.org/wiki/File:Lineweaver-Burke_plot.svg Interpreting LineweaverBurk Plots Consider enzymes A, B, and C: Which has the highest Vmax value? C Which has the highest Km value? B Which has the best affinity? A A 1/V B C -3 -2 -1 1/ [S] End of Prelearning Please complete the assignment for a completion check You will find it a ppt titled “kinetics prelearning assignment” in your course shell Instructions on how to post your answers will be posted to the course page later this week
