Catalase (EC 1.11.1.6) is a widespread enzyme, found in nearly all aerobic cells (animals, plants and microbes). It serves to protect the cell from toxic effects of hydrogen peroxide, generated as a by-product of cell metabolism. It does this by catalysing the decomposition of hydrogen peroxide into molecular oxygen and water.

This protocol uses a deceptively simple, yet very accurate method to measure the rate of reaction by collecting the oxygen evolved as a product of the reaction. The whole reaction can be carried out on a very small scale, in a centrifuge tube. An enzyme extract is adsorbed to filter paper discs. These discs initially sink in a hydrogen peroxide solution, but then float to the surface as the oxygen produced gets trapped in the paper fibres. The time taken for the discs to rise is measured.