The effect of pH on the rate of enzyme action

• what do most enzymes have?

  an optimum pH
• what is an optimum pH?

  where the rate of reaction is the highest
• what does small pH changes do to enzymes?

  it causes small reversible changes in enzyme structure and reduces its activity
• what happens to enzymes at extremes of pH?

  • the charges on the amino acid side-chains of the enzyme’s active site are affected by hydrogen ion or hydroxide ions
  • this disrupts the ionic and hydrogen bonds maintaining the shape of the active site
  • the shape changes, denaturing the enzyme
  • no enzyme-substrate complexes form and enzyme activity is lost
• what happens to enzymes at low pH?

  • excess $H^+$ions are attracted to negative charges and neutralise them
  • this disrupts the ionic and hydrogen bonds that maintain the shape of the active site
  • the shape changes, denaturing the enzyme
  • no more enzyme-substrate complexes form and the enzyme activity is lost
• what happens to enzymes at high pH?

  • excess $OH^-$ions neutralise the positive charges
  • this disrupts the ionic and hydrogen bonds that maintain the shape of the active site
  • the shape changes, denaturing the enzyme
  • no enzyme-substrate complexes are formed and enzyme activity is lost
• what does this graph show?

  effect of pHon rate of reaction