Homogeneous enzyme-linked assays mediated by enzyme antibodies; a new approach to electrode-based immunoassays

Abstract

A new homogeneous enzyme--immunoassay system is described. The assay employs an ammonia-liberating enzyme covalenty coupled to protein antigens along with two antibodies. An anti-enzyme antibody inhibits the enzyme. However, an antibody selective for the antigen reverses the inhibition process. When samples containing free antigen are present in the assay mixture, there is competition for anti-antigen antibody sites and protection against the anti-enzyme antibodies is diminished. The extent of the enzymatic reaction is monitored with an ammonium ion-selective electrode. Preliminary data demonstrating the feasibility of this approach for human serum albumin are presented.