Streptavidin is a 66 kDa tetrameric protein purified from the bacterium Streptomyces avidinii, and exhibits high binding affinity to biotin. Each unit can bind one biotin. Horseradish peroxidase is metalloenzyme, a 44 kDa glycoprotein. When incubate with substrates, it produces a coloured, fluorimetric, or luminescent derivatives, which can be detected and quantified. HRP conjugated Streptavidin is widely used for the detection and quantification of biotinylated proteins.