title: The origins of unconjugated bilirubin in bile.
abstract: In order to investigate the origin of unconjugated bilirubin in bile, beta-glucuronidase activity in rat and human bile was determined at various pH. beta-Glucuronidase in rat and human bile had their optimum pH at 5.5 when phenolphthalein glucuronide and delta 1-azopigment were used as substrate, and at 6.0 when bile itself was incubated. In human and rat bile the hydrolysis was suppressed to a minimum at each physiologic pH. However, human bile shows remarkable hydrolysis in alkaline pH (7.5--8.0). On the other hand, when delta 1-azopigment was incubated in various buffers, several per cent of delta 1-azopigment were hydrolyzed non-enzymatically in neutral to alkaline pH. Thus, it was suggested that enzymatic and nonenzymatic hydrolysis contributes to the existence of unconjugated bilirubin in bile.
mesh_terms: D000818:Animals; D001391:Azo Compounds / Q000378:metabolism; D001646:Bile / Q000201:enzymology / Q000378:metabolism*; D001663:Bilirubin / Q000378:metabolism*; D005965:Glucuronates / Q000378:metabolism; D005966:Glucuronidase / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D066298:In Vitro Techniques; D010635:Phenolphthaleins / Q000378:metabolism
chemical_list: D001391:Azo Compounds; D005965:Glucuronates; D010635:Phenolphthaleins; C016651:phenolphthalein glucuronide; D005966:Glucuronidase; D001663:Bilirubin