Horseradish peroxidase: the analyst's friend.

HRP is a calcium-containing, extensively glycosylated, stable haemoprotein possessing four disulphide bridges and weighing 44 kDa. It is an oxidoreductase which can use a wide variety of hydrogen donors to reduce hydrogen peroxide. This gives rise to a range of colorimetric, fluorimetric, chemiluminescent and electrochemical assays for HRP activity. HRP is very widely used as an indicator in immunoassays, non-isotopic DNA probes, cytochemistry, bi-enzyme systems and biosensors. This is owing to its stability, high catalytic rates, ease of conjugation to other molecules and wide choice of assays of activity.