UPDATED BMS100_BCH1.09_W23_Kinetics 2 STUDENTS copy PDF

Application of Km: Assignment Review NAD+ Ethanol NAD+ NADH + H+ Acetaldehyde NADH + H+ Acetate E = aldehyde dehydrogenase Alcohol consumption https://freesvg.org/1455185701 Flushing Back to normal https://commons.wikimedia.org/wiki/File:Smiley_Face.JPG Application of Km and Vmax: Glucokin...

Application of Km: Assignment Review NAD+ Ethanol NAD+ NADH + H+ Acetaldehyde NADH + H+ Acetate E = aldehyde dehydrogenase Alcohol consumption https://freesvg.org/1455185701 Flushing Back to normal https://commons.wikimedia.org/wiki/File:Smiley_Face.JPG Application of Km and Vmax: Glucokinase Hexokinase (most tissues) contrasts to glucokinase (liver) in the following ways: Lower Vmax Lower Km It is turned off by high concentrations of glucose-6-P Take a moment to discuss the next 3 slides with your classmates Glucokinase and Hexokinase How does the liver fit into all this? Glucokinase is found here Nutrients absorbed from the intestine go here first Allows glucokinase to convert excess glucose from a meal to glycogen Why can’t other tissues convert excess glucose to glycogen? (Hint: What role does glucose-6-P play?) https://commons.wikimedia.org/wiki/File:Depiction_of_a_man_suffering_from_fatty_liver.png Glucokinase and Hexokinase So if hexokinase can’t do glycogenesis, what pathway does it feed into? How does this explain its low Km? Does it make sense that glucokinase has a higher Km? Why do you think hexokinase is inhibited by glucose-6-P, but glucokinase is not? Glucokinase and Hexokinase Let’s talk about Vmax High Vmax = high capacity to convert substrate to product Allows glucokinase to phosphorylate lots of glucose to glucose-6-P after a meal, so it can be stored as glycogen Review: What is significant about adding a P to glucose? High Glucose HK pathway used for energy - Runs until what happens? Glucose Glucose GK HK (-) Glucose-6-P Glycolysis Glycogenesis Glucose-6-P GK pathway used for storage - High Vmax: lots of glucose to G-6-P - Continues as long as glucose is high. Turns off when glucose is low again due to its …? Km: What else is it good for? Km also helps determine enzyme efficiency Kcat Km measures speed of P formation once ES has been made measures binding affinity of E and S to make ES E+S ES E+P Enzyme Efficiency Which is a more efficient enzyme: one with a larger or smaller value for Kcat/Km? Kcat Km measures speed of P formation once ES has been made measures binding affinity of E and S to make ES Enzyme Inhibition M & M kinetics also aids in the study of enzyme inhibition What are some applications of enzyme inhibition? Physiological feedback mechanisms What example of this did we just see? Clinical therapies Ex: Use of pharmaceuticals to inhibit viral enzymes from replicating in HIV Enzyme Inhibition Types Reversible inhibition Competitive, uncompetitive, noncompetitive Follow M & M kinetics Irreversible inhibition Inhibition of allosteric enzymes (multisubunit) Reversible Enzyme Inhibition: Competitive Competitive inhibition Reversible binding of the inhibitor to the active site of the enzyme I No product S Product https://commons.wikimedia.org/wiki/File:Enzyme_inhibition_schemes.pn Reversible Enzyme Inhibition: Competitive Example Methotrexate Used for chemotherapy Competitively inhibits the enzyme that helps convert folate (B9) into its coenzyme form FYI: E = dihydrofolate reductase Folate coenzymes normally feed into purine and pyrimidine production – what are these used for? How does methotrexate help prevent the spread of cancer cells? Reversible Enzyme Inhibition: Competitive Competitive inhibition Why doesn’t Vmax change? Does the affinity of the enzyme appear to go up or down in the presence of the inhibitor? Why? Kmapp or Ki https://commons.wikimedia.org/wiki/File:Enzyme_Inhibition_lineweaver-burk_plots.gif Reversible Enzyme Inhibition: Uncompetitive Uncompetitive Reversible binding of I to ES Rare Substrate Product formation Inhibitor No product formation https://commons.wikimedia.org/wiki/File:Enzyme_inhibition_schemes.pn Reversible Enzyme Inhibition: Uncompetitive Uncompetitive inhibition Is Vmax lower or higher with I? Why? Does the affinity of the enzyme appear to go up or down in the presence of the inhibitor? Why? https://commons.wikimedia.org/wiki/File:Enzyme_Inhibition_lineweaver-burk_plots.gif Reversible Enzyme Inhibition: Noncompetitive Noncompetitive Reversible binding of I to E or ES Example: Product inhibition G-6-P inhibition of hexokinase Substrate Product formation Inhibitor No product formation https://commons.wikimedia.org/wiki/File:Enzyme_inhibition_schemes.pn Irreversible Enzyme Inhibition Irreversible Occurs when an inhibitor forms a covalent bond with the active site of the enzyme Compare and contrast to competitive inhibition Examples Penicillin Blocks the enzyme required for synthesis of bacterial cell walls Lead poisoning Review: Pb+2 binds to sulfhydryl groups in an enzyme involved in heme synthesis Changes its shape so it no longer functions • How can this lead to anemia? Inhibition of Multi-subunit Allosteric Enzymes Multi-subunit allosteric enzymes Review: What happens when an activator, which could be the substrate, binds? What is the resulting shape of the binding graph? What effect would an inhibitor have on the graph? Enzyme Substrate Slow Faster Fastest Inhibition of Multi-subunit Allosteric Enzymes Sigmoidal graph Inhibitor produces a right shift Enzyme A Enzyme plus B inhibitor C Inhibition of Multi-subunit Allosteric Enzymes Example: phosphofructokinase 1 (PFK1) Review: What does this enzyme do? Binding of F-6-P to one subunit enhances binding of F-6P to other subunits Creates a sigmoidal graph Allosterically inhibited by ATP What does the term “allosteric inhibition” tell us about where ATP binds when it is acting as an inhibitor vs a substrate? How do you think the Km for these different sites compare?