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. 1998;12(4):242-9.
doi: 10.1002/(sici)1098-2825(1998)12:4<242::aid-jcla9>3.0.co;2-9.

Equivalent recognition of free and ACT-complexed PSA in a monoclonal-polyclonal sandwich assay is conferred by binding specificity of the monoclonal antibody

Z Zhou  1 , E G Armstrong, A Belenky, J V Freeman, K K Yeung
Affiliations

Equivalent recognition of free and ACT-complexed PSA in a monoclonal-polyclonal sandwich assay is conferred by binding specificity of the monoclonal antibody

Z Zhou et al. J Clin Lab Anal. 1998.

Abstract

The Bayer Immuno 1 PSA Assay measures free and ACT-complexed PSA on an equimolar basis, although it uses a monoclonal antibody (MM1) for capture and polyclonal antibodies for detection. Competitive inhibition studies using antibodies directed at various epitopes on PSA and PSA-ACT demonstrated that the capture antibody, MM1, does not bind to free PSA simultaneously with antibodies against Epitope E which is exposed only in free PSA. Affinity studies showed that the affinity constants of MM1 for both free PSA and PSA-ACT are similar. One explanation for the properties of MM1 is that it precludes the binding of antibodies to Epitope E due to steric hindrance. Alternatively, the binding of MM1 causes a conformation change within the free PSA molecule, so that Epitope E is altered in a way that causes a loss of binding affinity. The unusual properties of MM1 are responsible for the equimolar response of this monoclonal-polyclonal sandwich assay for free and ACT-complexed PSA.

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