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Clinical Chemistry, Vol 41, 1273-1282, Copyright © 1995 by American Association for Clinical Chemistry
Z Chen, A Prestigiacomo and TA Stamey
Department of Urology S287, Stanford University School of Medicine, Stanford University Medical Center, CA 94305-5118, USA.
We describe for the first time a protocol to purify to apparent homogeneity an in vitro-prepared complex of prostate-specific antigen (PSA) and alpha 1-antichymotrypsin (ACT) by using a combination of gel filtration and ion-exchange chromatography. The purity of the PSA-ACT complex was confirmed by gel electrophoresis and Western blot. The PSA- ACT complex was stable in the pH range 6.0 to 7.8; it was also stable in various matrices, temperatures, and high concentrations of salt. Purification of the PSA-ACT complex was highly reproducible. An absorptivity of 0.99 L x g-1 x cm-1 at 280 nm was assigned to the PSA- ACT complex, based on amino acid analysis. Because PSA and ACT bind in a 1:1 molar ratio, we determined the molecular mass of the PSA-ACT complex as the mass encoded by the cDNA of ACT (plus 26% carbohydrate) plus the molecular mass of PSA (28,430 Da), which totals 89,280 Da. Using this material, we made two common calibrators, one of 100% PSA- ACT complex and one of 90% PSA-ACT complex plus 10% free PSA by volume (90:10 calibrator). Substitution of these calibrators for the manufacturers' calibrators in nine commercial immunoassays substantially reduced differences between immunoassays, especially for serum PSA values between 4 and 10 micrograms/L. The 90:10 calibrator is recommended as a universal calibrator for international standardization of PSA immunoassays.
The following articles in journals at HighWire Press have cited this article:
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  B. Rafferty, P. Rigsby, M. Rose, T. Stamey, and R. Gaines Das Reference Reagents for Prostate-specific Antigen (PSA): Establishment of the First International Standards for Free PSA and PSA (90:10) Clin. Chem., September 1, 2000; 46(9): 1310 - 1317. [Abstract] [Full Text] [PDF]
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J. Peter, C. Unverzagt, and W. Hoesel Analysis of Free Prostate-specific Antigen (PSA) after Chemical Release from the Complex with {alpha}1-Antichymotrypsin (PSA-ACT) Clin. Chem., April 1, 2000; 46(4): 474 - 482. [Abstract] [Full Text] [PDF]
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M. P. Fox, A. A. Reilly, and E. Schneider Effect of the Ratio of Free to Total Prostate-specific Antigen on Interassay Variability in Proficiency Test Samples Clin. Chem., August 1, 1999; 45(8): 1181 - 1189. [Abstract] [Full Text] [PDF]
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H. Nagasaki, M. Watanabe, N. Komatsu, T. Kaneko, J. Y. Dube, T. Kajita, Y. Saitoh, and Y. Ohta Epitope Analysis of a Prostate-specific Antigen (PSA) C-Terminal-specific Monoclonal Antibody and New Aspects for the Discrepancy between Equimolar and Skewed PSA Assays Clin. Chem., April 1, 1999; 45(4): 486 - 496. [Abstract] [Full Text] [PDF]
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R. Junker, B. Brandt, C. Zechel, and G. Assmann Comparison of prostate-specific antigen (PSA) measured by four combinations of free PSA and total PSA assays Clin. Chem., September 1, 1997; 43(9): 1588 - 1594. [Abstract] [Full Text] [PDF]
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