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Complex formation between PSA isoenzymes and protease inhibitors
J Leinonen1, W M Zhang, U H Stenman
1Department of Clinical Chemistry, Helsinki University Central Hospital, Finland.
The Journal of Urology
|March 1, 1996
Summary
Alpha 2-macroglobulin (A2M) is the primary inhibitor of prostate-specific antigen (PSA) in circulation. Unlike alpha 1-antichymotrypsin (ACT), A2M effectively complexes with both free and nicked PSA, preventing its release.
Area of Science:
- Biochemistry
- Protease Inhibitor Interactions
- Biomarker Analysis
Background:
- Prostate-specific antigen (PSA) exists in various forms, including free and complexed with protease inhibitors.
- Understanding PSA-protease inhibitor interactions is crucial for accurate biomarker interpretation.
Purpose of the Study:
- To investigate the in vitro complex formation between prostate-specific antigen (PSA) isoenzymes and major protease inhibitors.
- To characterize the kinetics and extent of complex formation with alpha 1-antichymotrypsin (ACT) and alpha 2-macroglobulin (A2M).
Main Methods:
- Utilized ion exchange and hydrophobic interaction chromatography for PSA isoenzyme separation.
- Employed immunofluorometric assays (IFMA) to quantify free PSA, PSA-ACT complexes, and total PSA.
- Assessed complex formation with A2M by monitoring the loss of free PSA immunoreactivity.
Main Results:
- Complex formation between PSA and A2M was more rapid than with ACT.
- In plasma-like conditions, PSA predominantly formed complexes with A2M (66%) rather than ACT (17%).
- Nicked PSA showed a higher affinity for A2M (54-67%) compared to ACT (5-18%).
Conclusions:
- Alpha 2-macroglobulin (A2M) is identified as the major inhibitor of PSA in circulation.
- Nicked PSA can effectively bind to A2M, becoming inaccessible to antibodies, challenging previous assumptions.