Fluorometric assay of protein in native human bile

Proteins in human native bile samples were determined by a fluorometric assay. Results were compared to biliary proteins quantified by the Lowry and Bradford techniques. The mean protein concentrations in bile as determined by the Lowry, Bradford and fluorometric assays were respectively 7.26 +/- 4.52 (SD), 2.9 +/- 1.42, and 2.12 +/- 1.28 mg/ml (n = 27). Bilirubin was shown to significantly interfere with the Lowry and Bradford assays but not the fluorometric assay. Bile salts remaining in the trichloroacetic acid (TCA) precipitate did not interfere with the fluorometric assay. No cholesterol or phospholipid could be detected in the TCA preparation prior to protein analysis. Proteolytic digestion of proteins in native bile was shown to occur at 37 degrees C and to a lesser extent at 22 degrees C. The fluorometric protein assay is an easy and accurate method to quantitate proteins in native human bile.