ENZYMES 2: KINETICS AND INHIBITION. HLeeYu Jsuico Junsay Department of Chemistry School of Science and Engineering Ateneo de Manila University

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1 ENZYMES 2: KINETICS AND INHIBITION HLeeYu Jsuico Junsay Department of Chemistry School of Science and Engineering Ateneo de Manila University 1

2 REVIEW OF KINETICS (GEN CHEM II) 2

3 Chemical KineCcs How fast will the reaccon proceed? It is the study of reac>on rates. REACTION RATES is the change in the concentracon of a reactant or product with Cme (M/s) A B!me

4 Rate Laws Or Rate Equa>on expresses the rate as a funccon of reactant concentracons, product concentracons and temperature Rate = k A [ ] m [ B] n The order of the reaccon tells you by how much rate changes as you change a parccular concentracon

5 Factors AffecCng ReacCon Rates Concentra>on of reactants ConcentraCon Temperature Temperature Physical State: Surface Area Rate of reaccon Rate of reaccon Surface area of solid or liquid Catalysis Presence of catalyst (light, compounds) Rate of reaccon Rate of reaccon

6 Collision Theory Atoms and Molecules must collide. Affected by concentracon Affected by temperature They must collide with enough energy Affected by temperature They must collide in the proper orientacon

7 The balanced chemical equation provides information about the beginning and end of reaction. WHAT The reaction mechanism gives the path of the reaction. HOW Mechanisms provide a very detailed picture of which bonds are broken and formed during the course of a reaction.

8 ReacCon Mechanisms Mechanism of α Chymotrypsin 1 1 Bugg, T An Introduc!on to Enzyme and Coenzyme Chemistry.

9 ReacCon Mechanisms The overall progress of a chemical reaccon can be represented at the molecular level by a series of simple elementary steps or elementary reac-ons. An elementary step is a process that occurs in a single event or step. The sequence of elementary steps that leads to product formacon is the reac-on mechanism. The molecularity is the number of molecules parccipacng in an elementary step (a single step!). unimolecular: one molecule in the elementary step, bimolecular: two molecules in the elementary step, and termolecular: three molecules in the elementary step. (not common, stacsccally improbable)

10 MulC step Mechanism Some reactions may take place in a series of elementary steps: 2NO (g) + O 2 (g) 2NO 2 (g) N 2 O 2 is detected during the reaction! Elementary step: NO + NO N 2 O 2 + Elementary step: N 2 O 2 + O 2 2NO 2 Overall reaction: 2NO + O 2 2NO 2 Elementary steps must add to give the balanced chemical equation. Intermediate : a species which appears in an elementary step which is not a reactant or product.

11 IdenCfying Intermediates Intermediates are species that appear in a reaction mechanism but not in the overall balanced equation. An intermediate is always formed in an early elementary step and consumed in a later elementary step. Elementary step: NO + NO N 2 O 2 + Elementary step: N 2 O 2 + O 2 2NO 2 Overall reaction: 2NO + O 2 2NO 2

12 Rate Laws of Elementary Step The rate law of an elementary step is determined by its molecularity: Unimolecular processes are first order Bimolecular processes are second order Termolecular processes are third order Unimolecular reaccon A products rate = k [A] Bimolecular reaccon A + B products rate = k [A][B] Bimolecular reaccon A + A products rate = k [A] 2

13 Why? Elementary steps are one step reaccons. However you change the concentracon of one species will directly affect the # of effeccve collisions.

14 HOW DO WE DESCRIBE ENZYME KINETICS? 14

15 Enzyme kineccs was described by Leonor Michaelis and Maud Menten: 15

16 Enzyme kineccs was described by Leonor Michaelis and Maud Menten: Enzymes (E) associate with their substrate (S) to form an Enzyme Substrate complex (ES), then ager forming the ES complex, enzyme works to form the products (P). E + S ES E + P k 1 k 2 k 3 k 4 16

17 Enzyme kineccs was described by Leonor Michaelis and Maud Menten: Experiments were ran with constant E and increasing S (similar to your Chem 12 experiments!) 17

18 Enzyme kineccs was described by Leonor Michaelis and Maud Menten: Using steady state assumpcons (concentracon of intermediates do not change with Cme) ( 1) [ E] T = [ E] + [ ES] (2) dp dt = v = k 0 3 [ ] ( 3) d ES dt ES [ ] = 0 = k 1 E [ ] S [ ] k 2 ES [ ] k 3 ES [ ] 18

19 Enzyme kineccs was described by Leonor Michaelis and Maud Menten: Using steady state assumpcons (concentracon of intermediates do not change with Cme), the following equacon was derived: Maximum velocity of enzyme catalysis [ ] v = v S MAX 0 K + S M [ ] Michaelis Menten constant 19

20 V MAX happens when all enzymes are being transformed to ES complexes that can create products. v = k [ E] MAX 3 T 20

21 V MAX happens when all enzymes are being transformed to ES complexes that can create products. v MAX = k 3 [ E] T High k 3 (some>mes called k cat ), High v MAX, good cataly>c ac>vity! 21

22 K M describes how well the enzyme is alached to the substrate (usually when a special case is adopted, k 2 >>>k 3 ). K M = k 2 + k 3 k 1 22

23 K M describes how well the enzyme is alached to the substrate (usually when a special case is adopted, k 2 >>>k 3 ). K M = k 2 + k 3 k 1 Low K M, Substrate is >ghtly bound to enzyme, MORE chances to produce products! 23

24 What happens when you change some parameters? As long as there is enough substrate, higher enzyme concentra>on, higher rate! 24

25 What happens when you change some parameters? Enzymes operate at specific/op>mum ph 25

26 What happens when you change some parameters? Increasing temperature may increase ac>vity un>l a certain point, aaer which, enzyme gets denatured 26

27 In summary: Enzyme* K M (mm) K cat (s 1 ) kcat/k M Catalase , 000, x Carbonic anhydrase 9 400, x 10 5 Chymotrypsin *given specific substrates Also, Enzymes operate under op>mal condi>ons: ph, temperature and concentra>ons 27

28 How do you get these parameters in a graph? 28

29 How do you get these parameters in a graph? V MAX k cat (if we know [E] T ) 29

30 How do you get these parameters in a graph? When K M = [S} v 0 = v MAX S S [ ] [ ] + [ S] v 0 = v MAX 2 K M is concentracon when V max is halved 30

31 How do you get these parameters in a graph? 31

32 How do you get these parameters in a graph? Lineweaver Burk plot 1 = K 1 M v v S 0 MAX [ ] + 1 v MAX y = m x + b 32

33 How do you get these parameters in a graph? Lineweaver Burk plot 1 = K 1 M v v S 0 MAX [ ] + 1 v MAX [S] μm V 0 (μm/min) /[S] μm 1 1/V 0 (min/μm)

34 How do you get these parameters in a graph? Ini>al rate vs. [S]

35 How do you get these parameters in a graph? /v vs. 1/S y = x R² =

36 Some enzymes do not STRICTLY obey the MM theorem. We call them allosteric enzymes More on that in the next chapter! 36

37 ENZYME INHIBITION 37

38 Molecules which hinder enzyme accvity are called inhibitors. Inhibitors: reduce enzyme accvity ALTERATION VIA Influence on BINDING or Influence on TURN OVER NO. May or may not resemble substrate (transi>on state analogs) and may not react or react very slow compared to substrate Can be used as probes for nature of accve site 38

39 Molecules which hinder enzyme accvity are called inhibitors. 39

40 Molecules which hinder enzyme accvity are called inhibitors. Can be reversible (noncovalent) or irreversible (covalent) 40

41 Molecules which hinder enzyme accvity are called inhibitors. SPECIFIC TYPES OF IRREV. INHIB. Group specific reagents Reacts with exact amino acids SUBSTRATE ANALOGS Analog binds covalently SUICIDE INHIBITION Inhibitor is processed, product inhibits covalently 41

42 Molecules which hinder enzyme accvity are called inhibitors. Both reversible and irreversible can act COMPETITIVELY NONCOMPETITIVELY UNCOMPETITIVELY Real world reac>ons are mixed with high character of a specific type 42

43 Molecules which hinder enzyme accvity are called inhibitors. Husband Substrate Child Product Wife Enzyme No child No Product Gardener fling Inhibitor 43

44 Compe>>ve inhibi>on occurs when Enzyme can bind to substrate (ES) or inhibitor (EI), but not at the same Cme. Inhibitor binds to the accve site. The moral inhibi>on. Only the partner OR the mistress 44

45 Compe>>ve inhibi>on occurs when Enzyme can bind to substrate (ES) or inhibitor (EI), but not at the same Cme. Inhibitor binds to the accve site. Increase in [S] will increase the chance of forming ES complex, THUS, inhibi>on may be relieved when there is high [S] 45

46 Compe>>ve inhibi>on increases K M but not V max. 46

47 Noncompe>>ve inhibi>on occurs when Inhibitor can bind to either E (forming EI), or to ES (forming ESI). Inhibitor binds to another part of the enzyme. The amoral inhibi>on The mistress doesn t care 47 if the partner is there or not. Can amach any>me.

48 Noncompe>>ve inhibi>on occurs when Inhibitor can bind to either E (forming EI), or to ES (forming ESI). Inhibitor binds to another part of the enzyme. Once Inhibitor binds, no more ac>vity is expected Thus, Inhibitor lowers [E] T.. 48

49 Noncompe>>ve inhibi>on lowers Vmax, but doesn t affect K M. 49

50 Uncompe>>ve inhibi>on occurs when Inhibitor can bind only to the ES complex (forming ESI). Inhibitor binds to another part of the enzyme. The immoral inhibi>on mistress only comes IF partner is there. 50

51 Uncompe>>ve inhibi>on occurs when Inhibitor can bind only to the ES complex (forming ESI). Inhibitor binds to another part of the enzyme. Increasing the [S] will just allow more ESI to form. 51

52 Uncompe>>ve inhibi>on changes both Vmax and K M. 52

53 In summary, 53