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Substrate concentration

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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The rate of an enzyme-catalyzed reaction increases to a maximum rate, Vmax, with increasing substrate concentration. Vmax represents saturation of the enzyme with substrate. Km, the Michaelis constant, represents substrate concentration which produces half of Vmax. It is a measure of affinity of the enzyme for its substrate: the smaller Km, the greater is the affinity.

Practically, this means:

  • high concentrations of substrate should be used when testing in vitro activity of an enzyme
  • Vmax and Km values can be determined in vitro and in vivo to compare the contribution of a given enzyme to a specified metabolic reaction
  • a plot of the reciprocal of substrate concentration (x axis) against reciprocal of rate of reaction (y axis) can give Vmax - the reciprocal of the y-axis intercept - and Km - the negative reciprocal of the x-axis intercept. This is termed a Lineweaver-Burk plot.

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