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the kinetic parameters of enzyme-induced reactions

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1 the kinetic parameters of enzyme-induced reactions
CP504 – ppt_Set 03 Enzyme kinetics and associated reactor design: Determination of the kinetic parameters of enzyme-induced reactions learn about the meaning of kinetic parameters learn to determine the kinetic parameters learn the effects of pH, temperature and substrate concentration on enzyme activity (or reaction rates) learn about inhibited enzyme kinetics learn about allosteric enzymes and their kinetics Prof. R. Shanthini Updated: 23 Nov 2012

2 Simple Enzyme Kinetics (in summary)
E + S ES E + P k2 which is equivalent to [E] S P S for substrate (reactant) E for enzyme ES for enzyme-substrate complex P for product Prof. R. Shanthini Updated: 23 Nov 2012

3 Simple Enzyme Kinetics (in summary)
rmaxCS rP = - rS = KM + CS where rmax = k3CE0 = kcatCE0 and KM = f(rate constants) rmax is proportional to the initial concentration of the enzyme KM is a constant Prof. R. Shanthini Updated: 23 Nov 2012

4 Simple Enzyme Kinetics (in summary)
-rs Catalyzed reaction Catalyzed reaction rmax - rS rmaxCS = KM + CS rmax uncatalyzed reaction 2 KM Cs Prof. R. Shanthini Updated: 23 Nov 2012

5 An exercise Consider an industrially important enzyme, which catalyzes the conversion of a protein substrate to form a much more valuable product.  The enzyme follows the Briggs-Haldane mechanism:                                An initial rate analysis for the reaction in solution, with E0 = 0.10 μM and various substrate concentrations S0, yields the following Michaelis-Menten parameters: Vmax = 0.60 μM/s; KM = 80 μM. A different type of experiment indicates that the association rate constant, k1, is k1 = 2.0 x 106 M-1s-1 (2.0 μM-1s-1). a. Estimate the values of k2 and k-1. b. On average, what fraction of enzyme-substrate binding events result in product formation? Prof. R. Shanthini Updated: 23 Nov 2012 Source: Jason Haugh, Department of Chemical & Biomolecular Engineering, North Carolina State University

6 Simple Enzyme Kinetics (in summary)
Catalytic step k1 k3 E + S ES E + P k2 Substrate binding step k3 = kcat Prof. R. Shanthini Updated: 23 Nov 2012

7 learn about the meaning of kinetic parameters
learn to determine the kinetic parameters learn the effects of pH, temperature and substrate concentration on enzyme activity (or reaction rates) learn about inhibited enzyme kinetics learn about allosteric enzymes and their kinetics Prof. R. Shanthini Updated: 23 Nov 2012

8 t Cs - rs given 10 15 rmaxCS - rS = KM + CS
How to determine the kinetic parameters rmax and KM ? Carry out an enzyme catalysed experiment, and measure the substrate concentration (CS) with time. t Cs - rs given 10 15 rmaxCS - rS = KM + CS Prof. R. Shanthini Updated: 23 Nov 2012

9 How to determine the M-M kinetics rmax and KM ?
Carry out an enzyme catalysed experiment, and measure the substrate concentration (CS) with time. t Cs - rs given 10 15 rmaxCS - rS = KM + CS Prof. R. Shanthini Updated: 23 Nov 2012

10 rmaxCS - rS = KM + CS = - rS CS rmax KM 1 + (14) = - rS 1 rmax KM + CS
We could rearrange rmaxCS - rS = KM + CS to get the following 3 linear forms: = - rS CS rmax KM 1 + (14) = - rS 1 rmax KM + CS (15) = - rS rmax KM - CS (16) Prof. R. Shanthini Updated: 23 Nov 2012

11 The Langmuir Plot CS KM 1 CS (14) = + - rS rmax rmax - rS CS 1 rmax
Prof. R. Shanthini Updated: 23 Nov 2012

12 Determine rmax more accurately than the other plots.
The Langmuir Plot CS KM 1 CS (14) = + - rS rmax rmax - rS CS 1 rmax Determine rmax more accurately than the other plots. - KM CS Prof. R. Shanthini Updated: 23 Nov 2012

13 The Lineweaver-Burk Plot
1 KM 1 1 (15) = + - rS rmax rmax CS - rS 1 KM rmax 1 - KM CS 1 Prof. R. Shanthini Updated: 23 Nov 2012

14 The Lineweaver-Burk Plot
1 KM 1 1 (15) = + - rS rmax rmax CS - rS 1 Gives good estimates of rmax, but not necessarily KM - Data points at low substrate concentrations influence the slope and intercept more than data points at high Cs KM rmax 1 - KM CS 1 Prof. R. Shanthini Updated: 23 Nov 2012

15 The Eadie-Hofstee Plot
- rS - rS rmax = - KM (16) CS - rS KM rmax KM CS -rS Prof. R. Shanthini Updated: 23 Nov 2012

16 The Eadie-Hofstee Plot
- rS - rS rmax = - KM (16) CS - rS Can be subjected to large errors since both coordinates contain (-rS) - Less bias on point at low Cs than with Lineweaver-Burk plot KM rmax KM CS -rS Prof. R. Shanthini Updated: 23 Nov 2012

17 Data: CS (mmol/l) rS (mmol/l.min) 1 0.20 2 0.22 3 0.30 5 0.45 7 0.41 10 0.50 Determine the M-M kinetic parameters for all the three methods discussed in the previous slides. Prof. R. Shanthini Updated: 23 Nov 2012

18 rmax = 1 / slope = 1 / 1.5866 = 0.63 mmol/l.min
KM = rmax x intercept = 0.63 x = 2.93 mmol/l Prof. R. Shanthini Updated: 23 Nov 2012

19 rmax = 1 / intercept = 1 / 1.945 = 0.51 mmol/l.min
KM = rmax x slope = 0.51 x = 1.78 mmol/l Prof. R. Shanthini Updated: 23 Nov 2012

20 rmax = intercept = 0.54 mmol/l.min
KM = - slope = 1.89 mmol/l Prof. R. Shanthini Updated: 23 Nov 2012

21 The Lineweaver-Burk Plot The Eadie-Hofstee Plot
Comparison of the results The Langmuir Plot The Lineweaver-Burk Plot The Eadie-Hofstee Plot rmax KM R2 Prof. R. Shanthini Updated: 23 Nov 2012

22 The Lineweaver-Burk Plot The Eadie-Hofstee Plot
Comparison of the results The Langmuir Plot The Lineweaver-Burk Plot The Eadie-Hofstee Plot rmax 0.63 0.51 0.54 KM 2.93 1.78 1.89 R2 94.9% 84.6% 66.2% Prof. R. Shanthini Updated: 23 Nov 2012

23 The Lineweaver-Burk Plot The Eadie-Hofstee Plot
Comparison of the results The Langmuir Plot The Lineweaver-Burk Plot The Eadie-Hofstee Plot rmax 0.63 0.51 0.54 KM 2.93 1.78 1.89 R2 94.9% 84.6% 66.2% Determine rmax more accurately than the other plots Gives good estimates of rmax, but not necessarily KM Can be subjected to large errors Prof. R. Shanthini Updated: 23 Nov 2012

24 learn about the meaning of kinetic parameters
learn to determine the kinetic parameters learn the effects of pH, temperature and substrate concentration on enzyme activity (or reaction rates) learn about inhibited enzyme kinetics learn about allosteric enzymes and their kinetics Prof. R. Shanthini Updated: 23 Nov 2012

25 Effects of temperature on enzyme activity:
Increases in the temperature of a system results from increases in the kinetic energy of the system. Kinetic energy increase has the following effects on the rates of reactions: More energetic collisions Increase in the number of collisions per unit time Denaturation of the enzyme or substrate Prof. R. Shanthini Updated: 23 Nov 2012

26 Effects of temperature on enzyme activity:
More energetic collisions: When molecules collide, the kinetic energy of the molecules can be converted into chemical potential energy of the molecules. If the chemical potential energy of the molecules become great enough, the activation energy of a exergonic reaction can be achieved and a change in chemical state will result. Thus the greater the kinetic energy of the molecules in a system, the greater is the resulting chemical potential energy when two molecules collide. As the temperature of a system is increased it is possible that more molecules per unit time will reach the activation energy. Thus the rate of the reaction may increase. Prof. R. Shanthini Updated: 23 Nov 2012

27 Effects of temperature on enzyme activity:
Increase in the number of collisions per unit time: In order to convert substrate into product, enzymes must collide with and bind to the substrate at the active site. Increasing the temperature of a system will increase the number of collisions of enzyme and substrate per unit time. Thus, within limits, the rate of the reaction will increase. Prof. R. Shanthini Updated: 23 Nov 2012

28 Effects of temperature on enzyme activity:
Denaturation of the enzyme: Enzymes are very large proteins whose three dimensional shape is vital for their activity. When proteins are heated up too much they vibrate. If the heat gets too intense then the enzymes literally shake themselves out of shape, and the structure breaks down. The enzyme is said to be denatured. A denatured enzyme does not have the correct 'lock' structure. Therefore it cannot function efficiently by accepting the 'key' substrate molecule. Prof. R. Shanthini Updated: 23 Nov 2012

29 Effects of temperature on enzyme activity:
Denaturation of the enzyme: Prof. R. Shanthini Updated: 23 Nov 2012

30 Effects of temperature on enzyme activity:
Denaturation of the enzyme: As temperature increases, enzyme activity increases until its optimum temperature is reached. At higher temperatures, the enzyme activity rapidly falls to zero. Prof. R. Shanthini Updated: 23 Nov 2012

31 Effects of temperature on enzyme activity:
Denaturation for most human enzymes: The optimum temperature for most human enzymes to work at is around 37ºC which is why this temperature is body temperature. Enzymes start to denature at about 45°C. Optimal for most human enzymes Prof. R. Shanthini Updated: 23 Nov 2012

32 Effects of temperature on enzyme activity:
Optimal for most human enzymes Optimal for some thermophillic bacterial enzymes Reaction rate Temperature (deg C) Prof. R. Shanthini Updated: 23 Nov 2012

33 Effects of pH on enzyme activity:
The structure of the protein enzyme can depends on how acid or alkaline the reaction medium is, that is, it is pH dependent. If it is too acid or too alkaline, the structure of the protein is changed and it is 'denatured' and becomes less effective. If the enzyme does not have the correct 'lock' structure, it cannot function efficiently by accepting the 'key' substrate molecule. In the optimum pH range, the enzyme catalysis is at its most efficient. Prof. R. Shanthini Updated: 23 Nov 2012

34 Effects of pH on enzyme activity:
Optimal for pepsin (a stomach enzyme) Optimal for trypsin (an intestinal enzyme) Reaction rate pH Prof. R. Shanthini Updated: 23 Nov 2012

35 Effects of pH on enzyme activity:
Amylase (pancreas) enzyme Optimum pH: Function: A pancreatic enzyme that catalyzes the breakdown/hydrolysis of starch into soluble sugars that can readily be digested and metabolised for energy generation. Amylase (malt) enzyme Optimum pH: Function: Catalyzes the breakdown/hydrolysis of starch into soluble sugars in malt carbohydrate extracts. Prof. R. Shanthini Updated: 23 Nov 2012

36 Effects of pH on enzyme activity:
Catalase enzyme Optimum pH: ~7.0 Function: Catalyses the breakdown of potentially harmful hydrogen peroxide to water and oxygen. Important in respiration/metabolism chemistry. 2H2O2(aq) ==> 2H2O(l) + O2(g) Prof. R. Shanthini Updated: 23 Nov 2012

37 Effects of pH on enzyme activity:
Invertase enzyme Optimum pH: 4.5 Function: Catalyses the breakdown/hydrolysis of sucrose into fructose + glucose, the resulting mixture is 'inverted sugar syrup'. C12H22O11 + H2O ==> C6H12O6 + C6H12O6 Prof. R. Shanthini Updated: 23 Nov 2012

38 Effects of pH on enzyme activity:
Lipase (pancreas) enzyme Optimum pH: ~8.0 Function: Lipases catalyse the breakdown dietary fats, oils, triglycerides etc. into digestible molecules in the human digestion system. Lipase (stomach) enzyme Optimum pH: Function: As above, but note the significantly different optimum pH in the acid stomach juices, to optimum pH in the alkaline fluids of the pancreas. Prof. R. Shanthini Updated: 23 Nov 2012

39 Effects of pH on enzyme activity:
Maltase enzyme Optimum pH: Function: Breaks down malt sugars. Prof. R. Shanthini Updated: 23 Nov 2012

40 Effects of pH on enzyme activity:
Pepsin enzyme Optimum pH: Function: Catalyses the breakdown/hydrolysis of proteins into smaller peptide fragments. Prof. R. Shanthini Updated: 23 Nov 2012

41 Effects of pH on enzyme activity:
Trypsin enzyme Optimum pH: Function: Catalyses the breakdown/hydrolysis of proteins into amino acids. Note again, the significantly different optimum pH to similarly functioning pepsin. Prof. R. Shanthini Updated: 23 Nov 2012

42 Effects of pH on enzyme activity:
Urease enzyme Optimum pH: ~7.0 Function: Catalyzes the breakdown of urea into ammonia and carbon dioxide. (NH2)2(aq) + H2O(l) ==> 2NH3(aq) + CO2(aq) Prof. R. Shanthini Updated: 23 Nov 2012

43 Effects of substrate concentration on enzyme activity:
Prof. R. Shanthini Updated: 23 Nov 2012

44 Effect of shear Prof. R. Shanthini Updated: 23 Nov 2012

45 Complex enzyme kinetics
learn about the meaning of kinetic parameters learn to determine the kinetic parameters learn the effects of pH, temperature and substrate concentration on enzyme activity (or reaction rates) learn about inhibited enzyme kinetics learn about allosteric enzymes and their kinetics Prof. R. Shanthini Updated: 23 Nov 2012

46 Inhibited enzyme reactions
Inhibitors are substances that slow down the rate of enzyme catalyzed reactions. There are two distinct types of inhibitors: - Irreversible inhibitors form a stable complex with enzymes and reduce enzyme activity (e.g. lead, cadmium, organophosphorous pesticide) - Reversible inhibitors interact more loosely with enzymes and can be displaced. Prof. R. Shanthini Updated: 23 Nov 2012

47 Inhibited enzyme reactions - applications
Many drugs and poisons are inhibitors of enzymes in the nervous system. Poisons: snake bite, plant alkaloids and nerve gases Medicines: antibiotics, sulphonamides, sedatives and stimulants Prof. R. Shanthini Updated: 23 Nov 2012

48 Primary constituents of Snake Venom
Enzymes - Spur physiologically disruptive or destructive processes. Proteolysins - Dissolve cells and tissue at the bite site, causing local pain and swelling. Cardiotoxins - Variable effects, some depolarise cardiac muscles and alter heart contraction, causing heart failure. Harmorrhagins - Destroy capillary walls, causing haemorrhages near and distant from the bite. Coagulation - Retarding compounds prevent blood clotting. Thromboses - Coagulate blood and foster clot formation throughout the circulatory system. Haemolysis - Destroy red blood cells. Cytolysins - Destroy white blood cells. Neurotoxins - Block the transmission of nerve impulses to muscles, especially those associated with the diaphragm and breathing. Prof. R. Shanthini Updated: 23 Nov 2012

49 Inhibited enzyme reactions
Inhibitors are also classified as competitive and non-competitive inhibitors. Prof. R. Shanthini Updated: 23 Nov 2012

50 Competitive inhibition
- The structure of inhibitor molecule closely resembles the chemical structure and molecular geometry of the substrate. - The inhibitor competes for the same active site as the substrate molecule. It does not alter the structure of the enzyme. The inhibitor may interact with the enzyme at the active site, but no reaction takes place. Prof. R. Shanthini Updated: 23 Nov 2012

51 Competitive inhibition
The inhibitor is "stuck" on the enzyme and prevents any substrate molecules from reacting with the enzyme. However, a competitive inhibition is usually reversible if sufficient substrate molecules are available to ultimately displace the inhibitor. Therefore, the amount of enzyme inhibition depends upon the inhibitor concentration, substrate concentration, and the relative affinities of the inhibitor and substrate for the active site. Prof. R. Shanthini Updated: 23 Nov 2012

52 Competitive inhibition
Competitive inhibitors (denoted by I) compete with substrate to occupy the active site of the enzyme. k1 k3 E + S ES E + P k2 k4 E + I EI k5 where rP = k3 CES (17) CE0 = CE + CES + CEI (18) Prof. R. Shanthini Updated: 23 Nov 2012

53 Competitive inhibition
Assuming rapid equilibrium, we get k1 CE CS = k2 CES k2 CE CS KM = = (19) k1 CES k4 CE CI = k5 CEI k5 CE CI KI = = (20) k4 CEI Prof. R. Shanthini Updated: 23 Nov 2012

54 Competitive inhibition
Combining (17) to (20), we get k3CE0CS rmaxCS rP = = (21) KM (1 + CI / KI) + CS KM,app + CS where rmax = k3CE0 (5) KM (1 + CI / KI) (22) KM,app = KM = k2 / k1 (6) KM,app > KM Prof. R. Shanthini Updated: 23 Nov 2012

55 Competitive inhibition The Lineweaver-Burk Plot
- rS 1 CI > 0 CI = 0 (no inhibitor) 1 - KM, app 1 - KM 1 rmax CS 1 Prof. R. Shanthini Updated: 23 Nov 2012

56 Competitive inhibition
In the presence of a competitive inhibitor, the maximal rate of the reaction (rmax) is unchanged, but the Michaelis constant (KM) is increased. Prof. R. Shanthini Updated: 23 Nov 2012

57 Competitive inhibition – an example
Ethanol is metabolized in the body by oxidation to acetaldehyde, which is a toxic compound and a known carcinogen. The enzyme alcohol dehydrogenase (ADH) converts ethanol into acetaldehyde plus two hydrogen atoms. Prof. R. Shanthini Updated: 23 Nov 2012

58 Competitive inhibition – an example
Acetaldehyde is generally short-lived; it is quickly broken down to a less toxic compound called acetate in a rapid reaction so that acetaldehyde does not accumulate in the body. . The enzyme aldehyde dehydrogenase (ALDH) converts acetaldehyde to acetyl (acetate) radical and a hydrogen atom. Prof. R. Shanthini Updated: 23 Nov 2012

59 Competitive inhibition – an example
A drug, disulfiram (Antabuse) inhibits the aldehyde dehydrogenase. Such inhibition results in the accumulation of acetaldehyde in the body. High levels of acetaldehyde act directly on the heart and blood vessels, causing flushing, a racing heartbeat and a drop in blood pressure that causes dizziness. Other unpleasant symptoms include headache, shortness of breath, palpitations, nausea and vomiting. This drug is sometimes used to help people overcome the drinking habit. Prof. R. Shanthini Updated: 23 Nov 2012

60 Non-competitive inhibition
- The structure of inhibitor molecule is entirely different from that of the substrate molecule. The inhibitor forms complex at a point other than the active site (remote from or very close to the active site). It does not complete with the substrate. It alters the structure of the enzyme in such a way that the substrate can no longer interact with the enzyme to give a reaction. Prof. R. Shanthini Updated: 23 Nov 2012

61 Non-competitive inhibition
Non competitive inhibitors are usually reversible, but are not influenced by concentrations of the substrate as is the case for a reversible competitive inhibitor.   Prof. R. Shanthini Updated: 23 Nov 2012

62 Non-competitive inhibition
k1 k3 E + S ES E + P k2 k4 E + I EI k5 k6 EI + S ESI k7 k8 ES + I ESI k9 Prof. R. Shanthini Updated: 23 Nov 2012

63 Non-competitive inhibition
We could drive the rate equation (given on the next page) assuming the following: k2 k7 = KIM = KM = k1 k6 k5 k9 = KMI = KI = k4 k8 Prof. R. Shanthini Updated: 23 Nov 2012

64 Non-competitive inhibition
rmax,appCS rP = (23) KM + CS where rmax rmax,app = (24) (1 + CI / KI) rmax = k3CE0 (5) KM = k2 / k1 (6) rmax,app < rmax Prof. R. Shanthini Updated: 23 Nov 2012

65 Non-competitive inhibition The Lineweaver-Burk Plot
- rS 1 CI > 0 1 rmax,app CI = 0 (no inhibitor) 1 - KM 1 rmax CS 1 Prof. R. Shanthini Updated: 23 Nov 2012

66 Non-competitive inhibition
In the presence of a non-competitive inhibitor, the maximal rate of the reaction (rmax) is lower but the Michaelis constant (KM) is unchanged. Prof. R. Shanthini Updated: 23 Nov 2012

67 Uncompetitive inhibition
k1 k3 E + S ES E + P k2 k4 ES + I ESI k5 Inhibitor can only bind to the enzyme-substrate complex, reversibly forming a nonproductive complex. Prof. R. Shanthini Updated: 23 Nov 2012

68 Uncompetitive inhibition
An uncompetitive inhibitor binds only to the enzyme-substrate complex preventing the formation or release of the enzymatic products. Unlike with competitive inhibition an uncompetitive inhibitor need not resemble the structure of the enzymes natural substrate. An uncompetitive inhibitor is most effective at high substrate concentration as there will be more enzyme-substrate complex for it to bind. Unlike with competitive inhibitors the effects of an uncompetitive inhibitor cannot be overcome by increasing the concentration of substrate. Prof. R. Shanthini Updated: 23 Nov 2012

69 Non-competitive inhibition
rmax,appCS rP = (23) KM + CS where rmax rmax,app = (24) (1 + CI / KI) rmax = k3CE0 (5) KM = k2 / k1 (6) rmax,app < rmax Prof. R. Shanthini Updated: 23 Nov 2012

70 Uncompetitive inhibition
rmax,appCS rP = (25) KM,app + CS where rmax rmax,app = (24) rmax,app < rmax (1 + CI / KI) (26) KM,app = KM / (1 + CI / KI) KM,app < KM rmax = k3CE0 (5) KM = k2 / k1 (6) Prof. R. Shanthini Updated: 23 Nov 2012

71 Uncompetitive inhibition
KM is reduced rmax is also reduced This is because the total ‘pool’ of enzymes available to react has been reduced, effectively our enzyme concentration has reduced. Can be explained by rmax = k3CE0 = kcatCE0 Prof. R. Shanthini Updated: 23 Nov 2012

72 Uncompetitive inhibition The Lineweaver-Burk Plot
- rS 1 CI > 0 1 rmax,app CI = 0 (no inhibitor) 1 - KM, app 1 CS 1 1 rmax - KM Prof. R. Shanthini Updated: 23 Nov 2012

73 Competitive versus Uncompetitive inhibition
Prof. R. Shanthini Updated: 23 Nov 2012

74 Mixed inhibition Prof. R. Shanthini Updated: 23 Nov 2012

75 An exercise The kinetic properties of the ATPase enzyme, isolated from yeast, which catalyzes the hydrolysis of ATP to form ADP and Pi, are assessed by measuring initial rates in solution, with various ATP concentrations S0 and a total ATPase concentration E0 = 0.60 μM.  From these experiments, it is determined that Vmax = 1.20 μM/s; KM = 40 μM. a. Calculate the values of kcat and the catalytic efficiency for ATPase under these conditions. b. An inhibitor molecule is added at a concentration of 0.1 mM, and the experiments are repeated.  The apparent Vmax and KM are now found to be 0.6 μM/s, and 20 μM, respectively.  Speculate on how this inhibitor works (i.e., specify which species are engaged by the inhibitor). Prof. R. Shanthini Updated: 23 Nov 2012 Source: Jason Haugh, Department of Chemical & Biomolecular Engineering, North Carolina State University

76 Substrate / Product inhibition
Either the substrate or product of an enzyme reaction inhibit the enzyme's activity. This inhibition may follow the competitive, uncompetitive or mixed patterns. In substrate inhibition there is a progressive decrease in activity at high substrate concentrations. Product inhibition is often a regulatory feature in metabolism and can be a form of negative feedback. Prof. R. Shanthini Updated: 23 Nov 2012

77 Substrate / Product inhibition
Prof. R. Shanthini Updated: 23 Nov 2012

78 Assignment Get the rate equations for substrate and product inhibition
Prof. R. Shanthini Updated: 23 Nov 2012

79 “Food for Thought” CS (mg/l) -rS (mg/l.h) 10 5 20 7.5 30 50 12.5 60
13.7 80 15 90 110 21.5 130 9.5 140 150 5.7 Problem 3.13 from Shuler & Kargi: The following substrate reaction rate (-rS) data were obtained from enzymatic oxidation of phenol by phenol oxidase at different phenol concentrations (CS). By plotting (-rS) versus (CS) curve, or otherwise, determine the type of inhibition described by the data provided? Prof. R. Shanthini Updated: 23 Nov 2012

80 Sigmoid/Hill kinetics
A particular class of enzymes exhibit kinetic properties that cannot be studied using the Michaelis-Menten equation. The rate equation of these unique enzymes is characterized by Sigmoid/Hill kinetics as follows: rmaxCSn The Hill equation rP = (27) K + CSn Hill constant Hill coefficient n = 1 gives Michaelis-Menten kinetics n > 1 gives positive cooperativity n < 1 gives negative cooperativity Prof. R. Shanthini Updated: 23 Nov 2012

81 Sigmoid/Hill kinetics
Examples of the “S-shaped” sigmoidal/Hill curve, which is different from the hyberbolic curve of M-M kinetics. n = 6 n = 4 n = 2 Prof. R. Shanthini Updated: 23 Nov 2012

82 Sigmoid kinetics rP CSn rmax K + CSn θ ln = n ln(CS) – ln (K) (28)
For an alternative formulation of Hill equation, we could rewrite (25) in a linear form as follows: rP CSn θ = = rmax K + CSn θ ln = n ln(CS) – ln (K) (28) 1 - θ Prof. R. Shanthini Updated: 23 Nov 2012

83 Allosteric enzyme Find out what it is on your own
Prof. R. Shanthini Updated: 23 Nov 2012


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