A simple micro-assay for inorganic phosphate

Modification of two assay procedures (Van Belle, H. (1970) Anal. Biochem. 33, 132–142 and Itaya, K., and Ui, M. (1966) Clin. Chim. Acta 14, 361) has allowed the development of a manual assay for inorganic phosphate of high simplicity and sensitivity. Total analysis requires only three reagents and is accomplished in less than 5 min, and smaples containing less than 1 μg/ml of inorganic phosphate may be detected. This assay retains a unique principle of the former two, complexation (instead of reduction) of the phosphomolybdate heteropoly complex with an appropriate triphenylmethane dye (malachite green, methyl green). Use of detergents has been eliminated and some further properties of the dyes, the assay, and the latter's applicability to a coupled enzyme system for phosphomonoester and phosphodiester analysis are discussed. Consideration is also given to the associated phenomena of transphosphorylation. (Dayan, J., and Wilson, I. B. (1964) Biochim. Biophys. Acta 81, 620–623).