Method for carrying out non-isotopic immunoassays, labeled analytes and kits for use in such assays

A non-isotopic competitive binding assay method for determining the amount of an analyte in a sample containing a known analyte in an unknown concentration, which comprises the steps of:

• (a) forming a reaction mixture by bringing together in a medium, (1) said sample, (2) polypeptide-labeled analyte, (3) an antibody specific for said analyte, (4) a polypeptide partner capable of non-covalently binding with the polypeptides of the polypeptide-labeled analyte to form a complex having catalytic activity, and (5) a substrate capable of being converted to a reporter molecule by the catalytic activity of said complex, said polypeptide-labeled analyte being capable of competitively binding to said antibody and to said polypeptide partner, said antibody inhibiting the formation of a catalytically active complex in the absence of analyte, the concentrations of said antibody, polypeptide partner and polypeptide-labeled analyte being such as to cause varying amounts of analyte in the sample to be directly related to the conversion of said substrate to said reporter molecule as a function of the catalytic activity of the complex;
• (b) measuring the conversion of said substrate to said reporter molecule in said reaction mixture, and
• (c) determining the amount of analyte in said sample by comparing the conversion of said substrate to said reporter molecule to conversions of said substrate to reporter molecule obtained with known concentrations of said analyte.