The excretion of bilirubin as a diglucuronide giving the direct van den Bergh reaction

Abstract

Pigment II, the direct-reacting pigment of human bile, when coupled with benzenediazonium chloride, forms azo pigment B, whereas bilirubin forms azo pigment A. A comparison of the properties of these 2 azo pigments indicates that pigment B is the ester glucuronide of pigment A. It is shown that bilirubin is excreted in human bile as an ester diglucuronide. The other direct-reacting bile pigment, pigment I, which occurs in serum and urine together with pigment n, is probably an ester monoglucuronide of bilirubin. The difference in the type of van den Bergh reaction, and in the physiological behavior of bilirubin and pigments I and II, can be accounted for by the fact that bilirubin is lipid-soluble, whereas the bilirubin glucuronides are water-soluble.