[Inorganic pyrophosphatase--a new enzyme label for biochemical analysis].

Inorganic pyrophosphatase isolated from Escherichia coli has been proposed as a label in heterogeneous enzyme immunoassays. The enzyme is remarkably stable and insensitive to sodium azide. Enzyme-antibody conjugates were prepared with glutaraldehyde and purified by gel filtration. Enzyme activity was measured by means of a sensitive colour reaction between phosphomolybdate and malachite green. A 5-10-fold increase is sensitivity in terms of absorbance readings was observed compared to peroxidase-based assays. The colour change (yellow/greenish blue) inherent in the use of pyrophosphatase as the labelling agent is highly suitable for visual analysis.