Measuring Enzyme Activity (CIE AS Biology)

• The progress of enzyme-catalysed reactions can be investigated by:
  • Measuring the rate of formation of a product using catalase
  • Measuring the rate of disappearance of a substrate using amylase

Investigating catalase activity

• In this investigation, the rate of product formation is used to measure the rate of an enzyme-controlled reaction:
  • Hydrogen peroxide is a common but toxic by-product of metabolism
  • This means it must be broken down quickly
  • Catalase is an enzyme found in the cells of most organisms that breaks hydrogen peroxide down into water and oxygen
  • Hydrogen peroxide and catalase are combined and the volume of oxygen generated is measured in a set time
  • The rate of reaction can then be calculated

Experimental set-up for investigating the rate of formation of a product using catalase

Investigating amylase activity

• In this investigation, the rate of substrate disappearance is used to compare rates of reaction under different conditions:
  • Amylase is a digestive enzyme that hydrolyses starch into maltose and glucose
  • Amylase functions best at pH 7 and 37^oC (all enzymes operate best under specific conditions)
  • Amylase and starch are combined and this reaction mixture is then tested for starch at regular time intervals
  • This can be done by taking samples from the reaction mixture at each time interval and adding each sample to some iodine in potassium iodide solution (starch forms a blue-black colour with this solution)
  • In this way, the time taken for starch to be broken down can be measured
  • The investigation can be repeated under a variety of conditions (eg. by altering pH or temperature) and the reaction rates can then be compared

Experimental set-up for investigating the rate of disappearance of a substrate using amylase