Clinical Chemistry
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Clinical Chemistry 48: 1257-1264, 2002;
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(Clinical Chemistry. 2002;48:1257-1264.)
© 2002 American Association for Clinical Chemistry, Inc.

Sensitive and Specific Enzymatic Assay for the Determination of Precursor Forms of Prostate-specific Antigen after an Activation Step

Pauliina Niemelä1a, Janita Lövgren1, Matti Karp1, Hans Lilja2 and Kim Pettersson1

1 Department of Biotechnology, University of Turku, Tykistökatu 6A 6th Floor, FIN-20520 Turku, Finland.

2 Department of Clinical Chemistry, Lund University, University Hospital Malmö, 20502 Malmö, Sweden.

aAuthor for correspondence. Fax 358-2-3338050; e-mail pauliina.niemela{at}utu.fi.

Background: The proteome of the serine protease prostate-specific antigen (PSA) and its enzymatic properties have been clarified only recently. We have developed a specific and sensitive method for the measurement of active PSA and used it to measure proPSA in blood.

Methods: We used the synthetic peptide KGISSQY, which possesses a PSA-specific cleavage site, as substrate. To ascertain the specificity of the assay, we used an anti-PSA monoclonal antibody that captures known forms of PSA. An activation step enabled us to measure proPSA by converting it to mature, active PSA.

Results: The detection limit of the optimized assay was 0.5 µg/L. In blood samples from patients, the activation step substantially increased the concentration of active PSA, thus showing the presence of proPSA in the samples. ProPSA was 0–79% (median, 45%) of the amount of free PSA in 15 samples with total PSA concentrations of 5.3–423 µg/L. In samples obtained from three benign prostatic hyperplasia (BPH) patients after transurethal resection of the prostate, no significant increase in activity was detected after the activation step, thus showing that proPSA was not a portion of free PSA in plasma of BPH patients.

Conclusions: Proforms of PSA are a considerable fraction of free PSA in the blood of patients with increased total PSA. The approach described can be used to study the diagnostic value of proPSA and active PSA in patients with BPH and prostate cancer.




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P. Wu, L. Zhu, U.-H. Stenman, and J. Leinonen
Immunopeptidometric Assay for Enzymatically Active Prostate-Specific Antigen
Clin. Chem., January 1, 2004; 50(1): 125 - 129.
[Abstract] [Full Text] [PDF]


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