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Enzymes

Enzymes. Fall 2007 Lecture 2. Enzymes. High molecular weight proteins 15,000 < MW <4,000,000 Catalysts Nomenclature - end with “ase” Holoenzyme - enzyme containing a non-protein group like a metal (apoenzyme + cofactor) (protein + metal) Isoenzymes - catalyze same rxn

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Enzymes

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  1. Enzymes Fall 2007 Lecture 2 Downloaded from www.pharmacy123.blogfa.com

  2. Enzymes • High molecular weight proteins 15,000 < MW <4,000,000 • Catalysts • Nomenclature - end with “ase” • Holoenzyme - enzyme containing a non-protein group like a metal • (apoenzyme + cofactor) • (protein + metal) • Isoenzymes - catalyze same rxn • Classified based on type of rxn catalyzed (Table 3.1) Downloaded from www.pharmacy123.blogfa.com

  3. Examples(enzyme - use - source) • Trypsin - anti-inflammatory, meat tenderizers - animal pancreas • amylase - syrup, glucose production - Bacillus subtilis • protease - detergents, silver recovery - B. subilis • invertase - confectionaries- Sacharomyces cerevisiae • cellulase - breaks down cellulose - bacteria/yeast/mold • penicillinase - remove penicillin from allergic individuals - bacteria Downloaded from www.pharmacy123.blogfa.com

  4. Enzyme Function • Lower activation energy of a reaction by binding to the substrate and forming a substrate-enzyme complex • Interaction is due to van der Waals and H-bonding at the active site • Interaction is complex - studied via Raman Spectroscopy and X-ray • Enzyme does not affect equilibrium constant or free energy change Downloaded from www.pharmacy123.blogfa.com

  5. Lowers the activation energy of a reaction - highly specific Downloaded from www.pharmacy123.blogfa.com

  6. Lock and Key Mechanism Specific binding site Downloaded from www.pharmacy123.blogfa.com

  7. Enzyme Kinetics E S P r = v = dP/dt = k1(S) S + E P + E r = v = dP/dt = k1(S)(E) Zero order First order Downloaded from www.pharmacy123.blogfa.com

  8. Enzyme Kinetics Michaelis Menten Approach (Henri) S + E <------------> ES -----------> E + P Based on experimental data k1 k3 k2 Downloaded from www.pharmacy123.blogfa.com

  9. Rapid Equilibrium MM k1 (E)(S) = k2(ES) or (1) Rate Equation (2) substituting for (ES) from Eq 1 into Eq 2 Downloaded from www.pharmacy123.blogfa.com

  10. Using the total enzyme balance E0 = E + ES or substituting into the rate equation Downloaded from www.pharmacy123.blogfa.com

  11. we obtain KM = k2/k1here is a dissociation constant, it characterizes the interaction of an enzyme with a given substrate S= KM when v = ½ vmax vmax= k3E0 - maximum reaction rate, proportional to the initial enzyme concentration Downloaded from www.pharmacy123.blogfa.com

  12. Vmax and KM Figure 3.3 in book Vmax KM Downloaded from www.pharmacy123.blogfa.com

  13. In many cases the assumption of rapid equilibrium is not valid although the enzyme-substrate reaction still shows saturation type kinetics. • In Class Exercise S + E <----------> ES <-----------> E + P Assume rapid equilibrium and determine the rate expression for product formation k3 k1 k4 k2 Downloaded from www.pharmacy123.blogfa.com

  14. Quasi Steady State Approach • Briggs and Haldane – another mathematical approach to the observed experimental MM eqn S + E <--------> ES-----------> E + P Assume that the change in (ES) with time is very small compared with to changes in S or P Rate Equation of (ES) k3 k1 k2 Downloaded from www.pharmacy123.blogfa.com

  15. Hint: Solve SS eqn for whatever quantity set equal to zero Assuming quasi steady state d(ES)/dt = 0 Solve equation for (ES) Rate Equation for P is substituting for (ES) Using the total enzyme balance E0 = E + ES Downloaded from www.pharmacy123.blogfa.com

  16. Hint: Do not multiply through k values Or Substituting into the rate equation for E Rearranging results in the following: Downloaded from www.pharmacy123.blogfa.com

  17. The equation has the same form as the MM eqn Where vmax = k3E0 and Or Figure 3.4 • In Class Exercise S + E <----------> ES <-----------> E + P Assume rapid quasi steady state and determine the rate expression for product formation k3 k1 k4 k2 Downloaded from www.pharmacy123.blogfa.com

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