Preparation and characterization of xanthine oxidase-antibody and -hapten conjugates for use in sensitive chemiluminescent immunoassays.

Methods have been developed to label haptens or antibodies with xanthine oxidase for use in chemiluminescent enzyme immunoassays. We have optimised coupling reactions involving the use of heterobifunctional cross-linkers, the introduction of sulfhydryl groups and the utilization of accessible cysteine residues on the native enzyme. The versatility of xanthine oxidase as a label in immunoanalysis was studied in five assay systems, including both competition procedures (TT4 and direct serum estradiol assays) and immunometric assays (TSH, IgE, hCG). In all of the assay systems, the performance of the conjugates was excellent, demonstrating that the chelate enhanced luminometric detection of xanthine oxidase should have a wide potential in many immunoassays.