A universal calibrator for prostate specific antigen (PSAI)

We describe for the first time a protocol to purify an in vitro made PSA-ACT complex to apparent homogeneity by using a combination of gel filtration and ion-exchange chroma-tography. The purity of the PSA-ACT complex was confirmed by gel electrophoresis and Western blot. Purification of the PSA-ACT comlex was highly reproducible. An extinction coefficient of 1.0 and 280 nm (L x g−1 x cm−1) was assigned to the PSA-ACT complex based on amino acid analysis. Molecular weight was assigned by taking cDNA of ACT (plus 26% carbohydrate) and the molecular weight of PSA (28 430) which totals 89 280. Two common calibrators were made consisting of 100% PS A-ACT complex and/or 90% PSA-ACT complex plus 10% free PSA (90:10 calibrator). The 90:10 calibrator is recommended as a universal calibrator for the international standardization of PSA immunoas-says.