Enzyme Kinetics

Michaelis-Menten kinetics

For an enyzme reaction that obeys Michaelis-Menten kinetics:
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  • S: solute concentration
  • V0: initial rate (velocity) of reaction
  • VMAX: the maximum rate of reaction when all enzyme active sites are saturated with substrate velocity
  • Km (Michaelis constant): the substrate concentration that gives half maximal velocity
    • Km = [S] at 0.5(VMAX)
    • Low Km = enzyme only needs a small amount of substrate to work at half max velocity (+ reverse)

Calculating Km

  • Km = (k-1+k2)k1
    • k1 = forward rate for enzyme association with substrate
    • k-1 = backwards rate for enzyme dissociation with substrate
    • k2 = forward rate of enzyme conversion from energy to product

Lineweaver-Burk Plot

  • VMAX = intersection of line with Y axis
  • KM = intersection of line with X axis
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Enzyme inhibition

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Reversible inhibition

Competitive
  • Binds to active site
  • VMAX stays the same
  • Km varies
Non-competitive
  • Binds to allosteric site
  • Km stays the same
  • VMAX varies

Irreversible inhibition

  • Non-competitive - usually involves formation/breakage of covalent bonds in the enzyme complex

Enzyme regulation

  • Allosteric control - inhibition of rate limiting enzymes by end products
  • Sigmoidal curve
  • Example: binding of oxygen to haemoglobin