Read the summary and the most important questions on Laura's Medical biochemistry and pathophysiology

• 1 Enzymes and enzyme inhibitors

• 1.1 Basis concepts and enzyme kinetics

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• What are the 2 parameters that define an enzym-substraat reaction?

  1. Km: Interaction of enzyme with substrate (binding - reversible)
  2. Vmax, Kcat: The bound substrate is converted (catalysis - irreversible)

• Which reaction is reversible and irreversible in enzyme-catalysis ?

  S + E <=> ES → EP -> E + P
  
  

  • reversible: S + E <=> ES
  • irreversible: EP -> E + P

• For how many domain enzyme is the Michaelis-Menten kinetic equation for?What is the equation of Michaelis-Menten?What kind of curve does this equation represent?

  Michaelis-Menten kinetics for single-domain enzymes
  
  v = Vmax[S] / Km + [S]
  
  hyperbolic curve

• What are the inhibitors of Michaelis-Menten enzymes?

  Inhibitors that bind reversibly to enzymes
  

  • Competitive inhibitors: substrate and inhibitor bind the same substrate binding site   
  • increased Km, same Vmax
  • Ibuprofen, oseltamivir (transition-state analoge: chemical compounds with a chemical structure that resemble the transition state of a substrate molecule in an enzyme-catalysed chemical reaction. Enzyme inhibitors which resembled the transition state structure would bind more tightly to the enzyme than the actual substrate)

  
  

  • Noncompetitive inhibitors: bind at allosteric site (locations other that its active site)
  • decreased Vmax, same Km 
  • Echinocandines

  
  
  Inhibitors that bind irreversibly to enzymes
  

  • Irreversible inhibitors
  • decreased Vmax → fewer active enzymes
  • Aspirin 
  • Mechanism-based (suicide) inhibitors: penicillin

• What are allosteric enzymes and inhibitor?

  Allosteric enzymes are multi-domain enzymes (a single subunit with regulatory and catalytic domains) or multisubunit enzymes, such as dimer, trimer, and tetramers
  
  Allosteric inhibitors bind allosteric enzymes reversibly at an allosteric site (a site other than the active site) and change the enzyme conformation form a more-active, relaxed (R) state to a less-active, tense (T) state.
  
  

  • Competitive inhibition: inhibitor binds to an allosteric site and prevents the substrate from binding

  
  
  

  • Noncompetitive inhibition: inhibitor binds to an allosteric site, inhibiting enzyme activity: substrate can still bind but the enzyme cannot catalyse the reaction

• 1.2 Suicide inhibitors

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• What are suicide inhibitors?

  Suicide (mechanism-based) inhibitors are modified substrates that modify the active site of an enzyme. 
  

  1. Bind reversibly to the enzyme in the same way as substrates
  2. Enzyme's catalytic mechanisme generates a chemically reactive intermediate that inactivates the enzyme through a covalent modification → therefore work irreversibly

• 1.3 The family of CYP

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• What is a cytochrome (CYP)?

  CYO is a protein that transfers electrons, using heme (precursor to hemoglobin) as its prosthetic group

• What are the 2 groups of CYP proteins?

  • Metabolize xenobiotics (drugs, polluants, agrochemicals)
    
  • participate in key biosynthetic pathways (biosynthesis of sterols or vitamin D)

• What is a Cytochrome (CYP) P450?

  Cytochrome P450 is a family of cytochromes that absorbs light maximally ate 450nm when complexed in vitro with exogenous carbon monoxide

• 2 Drug development

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• What does ADME stand for?

  Absorption
  Distribution
  Metabolism
  Excretion
  
  ADME ("add me")
  
  The concentration o fa drug at its target compartment (yellow) depends on its ADME properties.