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Prostate-specific antigen forms a complex with and cleaves alpha 1-protease inhibitor in vitro
W M Zhang1, J Leinonen, N Kalkkinen
1Department of Clinical Chemistry, Helsinki University Central Hospital, Finland.
The Prostate
|October 8, 1997
Summary
Prostate-specific antigen (PSA) forms a slow, reversible complex with alpha 1-protease inhibitor (API) in vitro. This purified PSA-API complex is crucial for developing new diagnostic assays for prostate cancer.
Area of Science:
- Biochemistry
- Proteomics
- Cancer Diagnostics
Background:
- Prostate-specific antigen (PSA) and alpha 1-protease inhibitor (API) complexes are relevant for prostate cancer diagnosis.
- In vitro formation of pure PSA-API complexes was previously unachieved, hindering assay development.
Purpose of the Study:
- To achieve and characterize in vitro formation of prostate-specific antigen (PSA)-alpha 1-protease inhibitor (API) complexes.
- To establish methods for purifying PSA-API complexes for diagnostic assay development.
Main Methods:
- Incubation of PSA with excess API at 37°C.
- Quantification using immunofluorometric assays and characterization via SDS-PAGE, immunoblotting, and amino-acid sequencing.
- Purification using gel filtration and immunoaffinity chromatography.
Main Results:
- An 80-kDa SDS-stable one-to-one PSA-API complex formed slowly in vitro.
- Complex formation was only ~15% complete in 7 days, with API cleavage and loss of activity.
- Complex dissociation was observed, releasing active PSA and inactivated API, accelerated by serum.
Conclusions:
- PSA forms a reversible complex with API in vitro, though the reaction is slow and API is cleaved.
- Purified PSA-API facilitates the development of quantitative immunoassays for this complex.
- Understanding PSA-API complex dynamics is vital for prostate cancer diagnostics.