beta emission 40 or auger electron emission in the case of i 125 to stimulate the scintillation agent 1 to emit light photon emission 45 this light 45 is measured as counts in a beta plate counter when the tritiated peptide 35 is unbound it is too distant from the scintillation agent 1 and the energy is dissipated before reaching the bead 5 resulting in low measured counts non radioactive ligands which compete with the tritiated peptide 35 for the same binding site on the mutant phosphatase enzyme 30 will remove and or replace the tritiated peptide 35 from the mutant enzyme 30 resulting in lower counts from the uncompeted peptide control by varying the concentration of the unknown ligand and measuring the resulting lower counts the inhibition at 50 ic 50 for ligand binding to the mutant enzyme 30 can be obtained this then is a measure of the binding ability of the ligand to the mutant enzyme and the wild type enzyme the term 34 complex 34 as used herein refers to the assembly containing the mutant enzyme in its simplest embodiment the complex is a solid support with the mutant enzyme attached to the surface of the support a linker can also be employed as illustrated in fig1 the complex can further comprise a bead fluopolymer anti enzyme gst enzyme gst mutant enzyme ptp1 linking construct immunosorbent protein a and scintillation agent in general the complex requires a solid support beads immunoassay column of e g al 2 o 3 or silica gel to which the mutant enzyme can.