Function 
Horseradish peroxidase (HRP) catalyzes the oxidation of luminol to 3-aminophthalate using hydrogen peroxide.  The reaction is accompanied by emission of light.  In the presence of chemicals, particularly – p-iodophenol, the light emission is enhanced 1000-fold.  Upon addition of the proper substrate, the HRP complex emits colored light.  HRP contains a heme group[1].
  Relevance 
HRP isozyme C1a is widely used for detection of a labeled molecule to which it conjugates. 
  Structural highlights 
The active site contains a heme group and the substrate benzhydroxamic acid[2].