Enzyme Kinetics and Specificity: A Review of Enzyme Rates and Reactions, Lecture notes of Biochemistry

Download Enzyme Kinetics and Specificity: A Review of Enzyme Rates and Reactions and more Lecture notes Biochemistry in PDF only on Docsity! Review of Kinetics/Thermodynamics 1 Enzyme Rate (kun,uncat) Rate (kcat,enz) Ratio (kcat/ kun) Urease [3.5.1.5] 3x10-10 sec-1 3x104 sec-1 1x1014 Chymotrypsin [3.4.21.1] 1x10-10 sec-1 1x102 sec-1 1x1012 Hexokinase [2.7.1.1] 1x10-13 sec-1 1.3x10-3 sec-1 1x1010 Alcohol dehydrogenase [1.1.1.1] 6x10-12 sec-1 2.7x10-5 sec-1 4.5x106 Carbonic anhydrase [4.2.1.1] 1x10-2 sec-1 1x105 sec-1 1x107 Taken from Koshland, 1956 J . Cellular Comparative Physiology, Supp. 1, 47:217 Enzyme Activity 2 How do enzymes do their job? Different Models Hydrolase Enzymes Proteases Phospholipase Enzymes PLAD R [3.1.4.4] | | oe 6 \ Lyase: Pyruvate Decarboxylase [4.1.1.1] 6 Isomerase: Alanine Racemase [5.1.1.1] Basic Kinetics Zero, First, Second Order Rxns 7 Review of SN1 and SN2 Summary of Orders Order Eqn [Alinitiat [A]new (2x) Rate change ZeTO Rate=k[A]° 2M 4M no change Ist Rate=k[A] 2M 4M 2x 2nd Rate=k[A/? 2M 4M (2)?=4x 3rd Rate=k[A]§ 2M 4M (2)8=8x Order Eqn [Alinitiat [A]new (3x) Rate change zero Rate=k[A]° 1M 3M no change Ist Rate=k[A] IM 3M 3x ond Rate=K[AP? or [AB] IM 3M (3)2=9x 3rd Rate=k[A}* 1M 3M (3)8=27x 10 Low [S]?? High [S]?? Enzyme Rate vs. [S] Substrate molecule. Substrate concentration, (S] 11 12 Enzyme Kinetics -history -assumptions -derivation of Michaelis-Menten eqn Kal K, Values a Y:} Rn Enzymes Whose kcay/Km Approaches the Diffusion-Controlled Rate of Association with Substrate Enzyme Substrate carbonic anhydrase Catalase Crotonase Fumarate Triosephosphate Glyceraldehyde- 1.8X10-5 isomerase 3-phosphate* B-Lactamase Benzylpenicillin 2x 10-5 1108 Lineweaver-Burk Plot Slope =n Vmax x-intercept = a Vmax } 5 15 Competitive Inhibition 16 Pure Non-competitive Inhibition (Allosteric) Mixed Non-competitive Inhibition (Allosteric) (a) Ky< Ky (b) Ay< Ky 17