Inhibitor - BIOC 460, Spring 2008 Lecture 12 Enzymes:...

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BIOC 460, Spring 2008 LEC 12, Enzymes - Inhibition 1 Lecture 12 Enzymes: Inhibition 225-236 Problems: pp. 238-239, chapter 8, #1, 2, 4a,b, 5a,b, 7, 10 Jmol structure: cyclooxygenase/non-steroidal anti-inflammatory drugs: http://www. biochem . arizona .edu/classes/bioc462/462a/jmol/cox12/cox121. htm Key Concepts K m and V max can be determined from double reciprocal plots (1/V o vs. 1/[S]). Enzyme inhibitors: compounds that reduce velocity of enzyme-catalyzed reactions . 2 types: reversible and irreversible reversible inhibitors competitive : inhibitor ( I ) increases K m but has no effect on V max . uncompetitive: I decreases both K m and V max by same factor. pure noncompetitive : I decreases V max but has no effect on K m . – can distinguish different types of reversible inhibitors using double reciprocal plots (1/V o vs. 1/[S]) in absence of I and in presence of different concentrations of I. Irreversible inhibitors – cause irreversible (generally covalent) modification of the enzyme, inactivating it. several types: group-specific chemical modifying reagents that would react with certain types of functional groups on many different enzymes substrate analogs with a reactive group on them (so more specific for one enzyme) "suicide" substrates (mechanism-based inhibitors): not reactive until the specific chemical mechanism of their target enzyme makes them "kill" (covalently modify) the active site they're in.
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BIOC 460, Spring 2008 LEC 12, Enzymes - Inhibition 2 Key Concepts, continued Both reversible and irreversible inhibitors very helpful for: – providing information about shape of active site and types of amino acid side chains there – working out enzyme mechanisms – providing info about control of metabolic pathways – design of drugs Learning Objectives Terminology : double reciprocal plot, reversible inhibition (competitive, pure noncompetitive, uncompetitive), irreversible inhibition, affinity label, transition state analog, suicide inhibition (mechanism-based inhibitor) Given a hyperbolic V o /V max vs. [S] plot, explain the meaning of the ratio V o /V max in terms of occupied active site concentration and total active site concentration, and find K m directly from the graph, including its units. Given a Lineweaver-Burk plot (1/V o vs. 1/[S]), find/calculate V max and K m from the graph. Learning Objectives, continued Explain competitive, uncompetitive, and pure noncompetitive inhibition in terms of a diagram of linked reaction equilibria for formation of ES, EI, and (if it can form) EIS. (See Berg et al., Figs. 8-17, 8-18, 8-19.) Explain how these 3 types of inhibition can be distinguished from each other graphically: a) on a V o vs. [S] plot, and b) on a double reciprocal (Lineweaver-Burk) plot. What is the effect of a
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Inhibitor - BIOC 460, Spring 2008 Lecture 12 Enzymes:...

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