BIOCHEMISTRY: Allosteric enzymes – Flashcards
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Allosteric enzyme
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Enzymes that undergo a conformational change upon binding to an effector. This results in a change in binding affinity at a different ligand binding site More than 1 binding site More than one subunit
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Cooperativity
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The binding of one substrate molecule facilitates the binding of subsequent molecules to the enzyme MOST ALLOSTERIC ENZYMES DISPLAY POSITIVE COOPERATIVITY
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Hill equation
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"n" is the hill number It measures the degree of cooperativity n=1, no cooperativity n>1, (+) cooperativity n<1 (-) cooperativity
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Positive cooperativity
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Greater change in activity over a narrower range of [S] Enzyme without S bound is TENSE Enzyme bound to S is RELAXED
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Allosteric effectors
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Effectors may be positive (activators) or negative (inhibitors) 2 types of allosteric effectors
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2 types of allosteric effectors
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Homotropic effectors Heterotropic effectors
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Homotropic effectors
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Almost always positive (activators) A substrate binds to the active site and increases affinity of substrate to other active sites
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Heterotropic effectors
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Can be either negative (inhibitors) or positive (activators) Bind to allosteric site A regulatory molecule (NOT SUBSTRATE) that binds to an allosteric site and causes a conformational change of the enzyme Also changes the kinetic properties of the enzyme
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Allosteric activator
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An effector that binds the allosteric site and enhances the enzyme's activity
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Allosteric inhibitor
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An effector that binds the allosteric site and decreases the enzyme's activity
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2 types of heterotropic effectors
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V-system effectors K-system effectors
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V-system effectors
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Affect Vmax Activators increase Vmax Inhibitors decrease Vmax
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K-system effectors
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Affect K0.5 Activators decrease K0.5 Inhibitors increase K0.5
