THE PROTEIN-BINDING OF C14-BILIRUBIN IN HUMAN AND MURINE SERUM*

Abstract

Although at physiologic pH small amounts of unconjugated bilirubin are soluble in protein-free aqueous solutions (1), in plasma, virtually all pigment is bound to protein (2-4). In this inter- action of bilirubin with protein, albumin plays a major role (3-13), but some authors have sug- gested that, in addition, "specific" bilirubin-carrying proteins may exist in the a-or /-globulins (14-18). These reports disagree, however, about the precise globulin fraction involved, and other investigators (3, 5, 7-10, 12) have denied that bilirubin is bound by globulins. Resolution of this question is important because this transport process is believed to be one of the factors regu- lating the distribution of bilirubin between the blood and other organs, and governing the rate of pigment removal by the liver (19).