Quantification of subnanomolar amounts of phosphate bound to seryl and threonyl residues in phosphoproteins using alkaline hydrolysis and malachite green.

An assay for protein-bound phosphate with a capacity to determine 100 pmol of phosphate is described. It is based on the combination of two well known methods: the alkaline hydrolysis of phosphate from seryl and threonyl residues in phosphoproteins and the quantification of the released phosphate by the use of malachite green and phosphomolybdate.