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Process Kinetics

Process Kinetics. Lecture 1 Mahesh Bule. Introduction to Processes in Biofuel. Heterotrophic and phototrophic pathway for biofuel production. Important Process and Its Kinetics. Enzymatic hydrolysis Fermentation of soluble sugar Downstream e.g. extraction, purification etc.

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Process Kinetics

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  1. Process Kinetics Lecture 1 Mahesh Bule

  2. Introduction to Processes in Biofuel • Heterotrophic and phototrophic pathway for biofuel production

  3. Important Process and Its Kinetics • Enzymatic hydrolysis • Fermentation of soluble sugar • Downstream e.g. extraction, purification etc.

  4. Enzyme Kinetics • Enzymes are the agents of saccharification process • What we want to be able to determine: – Maximum velocity – Substrate affinity – Inhibitor affinity • What it can tell us: – Utilization of substrates • What can we do with the information: – Control and manipulate process

  5. Enzyme Kinetics Basics • Enzyme kinetics studies the reaction rates of enzyme-catalyzed reactions and how the rates are affected by changes in experimental conditions • An essential feature of enzyme-catalyzed reactions is saturation: at increasing concentrations of substrates the rate increases and approaches a limit where there is no dependence of rate on concentration

  6. Consideration of Enzyme Kinetics • Conformation of proteins and positions of side chains are important for enzyme-substrate interactions and catalysis. • Forces involved in protein folding and structure are also involved in catalysis- enzyme-substrate specificity • To use enzymes in biotechnology NEED TO KNOW KINETIC PARAMETERS OF THE ENZYME REACTION. • We may want enzymes that WORK FAST- convert more substrate in a fixed unit of time. To do this optimization we have to perform and analyze the enzyme catalyzed reaction. • You can adjust pH, temperature and add co-factors to optimize enzyme activity. • You cannot adjust substrate selectivity. • Just like chemical reactions, enzyme catalyzed reactions have kinetics and rates • Reaction kinetics is Michaelis-Menten kinetics.

  7. Important things to study • Michaelis-Menten kinetics • Interpretations and uses of the Michaelis-Menten equation • Enzyme inhibitors: types and kinetics

  8. Enzyme-substrate cycle

  9. Enzyme Kinetics Equation

  10. Michaelis-Menten Equation

  11. Initial Velocity (vo) and [S] • The concentration of substrate [S] present will greatly influence the rate of product formation, termed the velocity (v) of a reaction. Studying the effects of [S] on the velocity of a reaction is complicated by the reversibility of enzyme reactions, e.g. conversion of product back to substrate. • To overcome this problem, the use of initial velocity (vo) measurements are used. At the start of a reaction, [S] is in large excess of [P], thus the initial velocity of the reaction will be dependent on substrate concentration

  12. Michaelis-Menten Curve

  13. Substrate Saturation of an Enzyme A. Low [S] B. 50% [S] or Km C. High, saturating [S]

  14. Steady State Assumption • The M-M equation was derived in part by making several assumptions. An important one was: the concentration of substrate must be much greater than the enzyme concentration. • In the situation where [S] >> [E] and at initial velocity rates, it is assumed that the changes in the concentration of the intermediate ES complex are very small over time (vo). This condition is termed a steady-state rate, and is referred to as steady-state kinetics. Therefore, it follows thatthe rate of ES formation will be equal to the rate ES breakdown.

  15. Michaelis-Menten Equation Derivation • Rate of ES formation = k1([ET] - [ES])[S] (where [ET] is total concentration of enzyme E and k-2 is considered neglible) • Rate of ES breakdown to product = k-1[ES] + k2[ES]

  16. Michaelis-Menten Equation Derivation (cont) • Thus for the steady state assumption: • k1([ET] - [ES])[S] = k-1[ES] + k2[ES] • This equation is the basis for the final Michaelis-Menten following algebraic rearrangement and substitution of Km and Vmax terms.

  17. Vmax and Km [S] V0 = Vmax [S]+Km k-1 + k2 Km= k1 When V0=Vmax, Km= [S] Km is unique to each Enzyme and Substrate. It describes properties of enzyme-substrate interactions Independent of enzyme conc. Dependent on temp, pH etc. Vmax is maximal velocity POSSIBLE. It is directly dependent on enzyme conc. It is attained when all of the enzyme binds the substrate. (Since these are equilibrium reactions enzymes tend towards Vmax at high substrate conc but Vmax is never achieved. So it is difficult to measure). When an enzyme is operating at Vmax, all enzyme is bound to substrate and adding more substrate will not change rate of reaction (enzyme is saturated). (adding more enzyme will change the reaction).

  18. Important Conclusions of Michaels - Menten Kinetics • when [S]= KM, the equation reduces to • when [S] >> KM, the equation reduces to • when [S] << KM, the equation reduces to

  19. Vmax vo [Substrate] Measuring Km and Vmax 1/vo 1/Vmax 1/[S] -1/Km You can use a curve fitting algorithm to determine Km and Vmax from a V vs [S] plot (need a computer) Reaction rates are initial rates determined when the substrate is in vast excess and isn’t changing much. Alternatively you can convert the curve to a straight line via a double reciprocal plot (1/Vmax and 1/[S])

  20. Lineweaver – Burk Double Reciprocal Plots The Michaelis-Menten equation can be recast into a linear form To obtain parameters of interest Reciprocal form of equation 1 = Km 1 + 1 V Vmax S Vmax Y= m x + b The y-intercept gives the Vmaxvalue and the slope gives Km/Vmax Vmax is determined by the point where the line crosses the 1/Vi = 0 axis (so the [S] is infinite). Km equals Vmax times the slope of line. This is easily determined from the intercept on the X axis.

  21. Significance of Km and Vmax Km is [S] at 1/2 Vmax It is a constant for a given enzyme at a particular temp and pressure It is an estimate of equilibrium constant for substrate binding to enzyme Small Km= tight binding, large Km=weak binding It is a measure of substrate concentration required for effective catalysis Vmax is THEORETICAL MAXIMAL VELOCITY Vmax is constant for a given enzyme To reach Vmax, ALL enzyme molecules have to be bound by substrate Kcat is a measure of catalytic activity- direct measure of production of product under saturating conditions. Kcat is turnover number- number of substrate molecules converted to product per enzyme molecule per unit time Catalytic efficiency = kcat/km Allows comparison of effectiveness of an enzyme for different substrates

  22. A Hypothetical reaction

  23. Lock/Key or Induced Fit

  24. Lock/Key- Complementary shape The enzyme dihydrofolate reductase with its substrate NADP+ NADP+ binds to a pocket that is complementary to it in shape and ionic properties, an illustration of "lock and key" hypothesis of enzyme action. In reality, the complementarity between protein and ligand (in this case substrate) is rarely perfect,

  25. Induced Fit Hexokinase has a U-shaped structure (PDB ID 2YHX). The ends pinch toward each other in a conformational change induced by binding of D-glucose (red).

  26. Substrate specificity The specific attachment of a prochiral center (C) to an enzyme binding site permits enzyme to differentiate between prochiral grps

  27. Enzyme-substrate

  28. E E P S S E + S P E E E ES EP E + P Enzyme Inhibition

  29. +Inh Vmax 1/v -Inh -Inh +inh vo 1/Vmax 1/2 Vmax 1/[S] -1/Km -1/Km (app) [Substrate] Km Km (app) Competitive Inhibition • Inhibitor competes with substrates for binding to active site • Inhibitor is similar in structure to substrate, binds more strongly, reacts more slowly • Increasing [I] increases [EI] and reduces [E] that is available for substrate binding • Need to constantly keep [I] high for effective inhibition (cannot be metabolized away in body) • Slope is larger (multiplied by a) • Intercept does not change (Vmax is the same) • KM is larger (multiplied by a)

  30. Competitive Inhibition • Unimolecular Reaction • Bimolecular Reaction

  31. Uncompetitive Inhibition Binds only to ES complex but not free enzyme Binds at location other than active site Does not look like substrate. Binding of inhibitor distorts active site thus preventing substrate binding and catalysis Cannot be competed away by increasing conc of substrate (Vmax is affected by [I]) Increasing [I] lowers Vmax and lowers Km. • Increasing [I] • Lowers Vmax (y-intercept increases) • Lowers KM (x-intercept decreases) • Ratio of KM/Vmax is the same (slope)

  32. Uncompetitive Inhibition

  33. Mixed or Non Competitive Inhibition • Inhibitor binds E or ES • Increasing [I] • Lowers Vmax (y-intercept increases) • Raises KM (x-intercept increases) • Ratio of KM/Vmax is not the same (slope changes)

  34. Reversible Inhibition (non-competitive) A inhibitor binds the enzyme but not in its active site. It affects the Kcat because substrate can still bind the active site. Rate of catalysis is affected +Inh 1/v Vmax -Inh -Inh 1/Vmax (app) Vmax (app)_ +inh vo 1/2 Vmax 1/Vmax 1/2 Vmax (app) -1/Km 1/[S] [Substrate] Km Km (app) Vmax is decreased proportional to inhibitor conc

  35. Mixed Inhibition

  36. Kinetic modeling for enzymatic hydrolysis of pretreated creeping wild Ryegrass Refer article: Biotechnology and Bioengineering, Vol 102, No. 6, 2009, Page 1558-1568

  37. Homework: Reproduce model using Matlab

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