• All enzymes have an?optimum pH?or a pH at which they operate best
• Enzymes are?denatured?at extremes of pH
  • Hydrogen?and ionic bonds?hold the tertiary structure of the protein (ie. the enzyme) together
  • Below and above the optimum pH of an enzyme, solutions with an excess of H+?ions (acidic solutions) and OH-?ions (alkaline solutions) can cause these?bonds?to?break
  • This?alters the shape of the active site, which means enzyme-substrate complexes form less easily
  • Eventually, enzyme-substrate complexes can no longer form at all
  • At this point,?complete denaturation?of the enzyme has occurred
• Where an enzyme functions can be an indicator of its optimal environment:
  • Eg.?pepsin?is found in the stomach, an acidic environment at pH 2 (due to the presence of?hydrochloric acid?in the stomach’s gastric juice)
  • Pepsin’s optimum pH, not surprisingly, is pH 2

The effect of pH on the rate of an enzyme-catalysed reaction for three different enzymes (each with a different optimum pH)

• When investigating the effect of pH on the rate of an enzyme-catalysed reaction, you can use?buffer solutions?to measure the rate of reaction at?different pH values:
  • Buffer solutions each have a?specific pH
  • Buffer solutions?maintain?this specific pH, even if the reaction taking place would otherwise cause the pH of the reaction mixture to?change
  • A?measured volume?of the buffer solution is added to the reaction mixture
  • This?same volume?(of each buffer solution being used) should be added for each pH value that is being investigated