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Enzymology: 4. Kinetics & Inhibition

Enzymology: 4. Kinetics & Inhibition

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Enzyme Inhibition
Overview
KEY VALUES
  • Vmax
– Maximal rate of a reaction (every active site bound by substrate)
  • Km
– Inversely proportional to binding affinity of enzyme to substrate
ENZYME INHIBITION
  • Occurs when a substance reduces activity of an enzyme
Types of inhibition
  • Competitive
– Substrate & inhibitor compete for active site – Greater [S] overcomes inhibition – Increases the apparent Km but does NOT affect Vmax
  • Noncompetitive
– Inhibitor reversibly binds to enzyme outside of active site to deactivate it. – Enzymes regain function when inhibitor removed from system – Does NOT change Km but lowers Vmax
NOT uncompetitive inhibition in which inhibitors bind enzyme-substrate complexes
  • Uncompetitive inhibition: requires preassembled enzyme-substrate complexes-->more effective when [S] is high
  • Irreversible
– Inhibitor binds to and permanently deactivates enzyme – Only overcome by synthesis of new enzymes
CLINICAL CORRELATION
  • Heavy metals (mercury & lead)
– Irreversible inhibitors: bind tightly to sulfur groups in enzymes – Permanently deactivate them
  • Ethylene glycol (antifreeze) metabolites
– Toxic to human body – Ethanol (competitive inhibitor): used to inhibit alcohol dehydrogenase active site to prevent metabolism of ethylene glycol
  • Angiotension-converting enzyme (ACE) inhibitors
– Blood pressure lowering agents: noncompetitively inhibit ACE – Prevent formation of angiotensin (acts on kidneys to inc. blood pressure)

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