An array of chromogenic, fluorogenic and chemiluminescent substrates are available for use with HRP conjugated secondary antibodies HRP is a 40 kDa protein that catalyzes the oxidation of substrates by hydrogen peroxide, resulting in a colored or fluorescent product or the release of light as a byproduct of the reaction. HRP functions optimally at a near-neutral pH and can be inhibited by cyanides, sulfides and azides. Antibody-HRP conjugates are superior to antibody-AP conjugates with respect to the specific activities of both the enzyme and antibody. In addition, its high turnover rate, good stability, low cost and wide availability of substrates makes HRP the enzyme of choice for most applications. HRP can be used for chemiluminescent readout in western blot, colorimetric readout in ELISA, and precipitation reactions useful in immunocytochemistry and immunohistochemistry.