Phosphatase immunoassay using antibodies against bisphosphorylated substrates

In the present invention a process for detecting enzyme activity in an immunoassay is described, the process comprising the following steps: a) providing a protein, peptide or a derivative thereof comprising the sequence motif -Z-X-Y- or -Y-X-Z- wherein Z = an amino acid to be modified by the enzyme X = a sequence of between 0 and 1000 amino acids which may be the same or different Y = an affinity enhancer for the binding to an antibody as a substrate for the enzyme; b) incubating the protein, peptide or a derivative thereof with the enzyme to form a modified protein, peptide or a derivative thereof; c) adding the antibody having a specificity to the peptide, protein or a derivative thereof that has been modified at the amino acid in the Z position; and d) detecting the enzyme activity.ym