Use of biotinylated inorganic pyrophosphatase for detection of biotin bound to solid support

A colorimetric procedure to detect biotin bound to microtiter plates with a sensitivity down to 10(-16) mol was developed using biotinylated inorganic pyrophosphatase of Escherichia coli. Reaction of pyrophosphatase with 1 mM N-biotinyl-6-aminocaproic acid N-hydroxy-sulfonosuccinimide ester yielded a stable 87% active enzyme containing 5.6 mol biotin/mol. In the measurements of human immunoglobulin G, a biotinylated pyrophosphatase.streptavidin complex provided a sensitivity superior to that of conventional enzyme immunoassay due to low nonspecific binding. The new procedure was also more sensitive compared with that using biotinylated alkaline phosphatase. Together with high thermostability of pyrophosphatase and its substrate, low background staining allowed measurement of enzymatic activity to be performed at 60 degrees C for 4 h resulting in a marked increase in assay sensitivity.