title: Direct binding of ligandin to uridine 5'-diphosphate glucuronosyltransferase 1A1.
abstract: OBJECTIVE
  Bilirubin, a final degradation product of heme produced mainly in the spleen, is carried to the liver through its binding to albumin in the blood circulation. After its transport to hepatocytes, ligandin (glutathione S-transferase; GST) carries bilirubin to the endoplasmic reticulum (ER). uridine 5'-diphosphate-glucuronosyltransferase 1A1 (UGT1A1) glucuronidates bilirubin for solubilization in the ER.
  
  
  METHODS
  By GST pull-down and co-immunoprecipitation assays, GSTA2, a member of the alpha-class of GST, was observed to directly bind to UGT1A1 through the region present inside the ER.
  
  
  RESULTS
  GSTA2 was detected in the microsomal fraction together with the cytosolic fraction after hepatocyte fractionation.
  
  
  CONCLUSIONS
  These results strongly suggest that bilirubin is directly delivered to UGT1A1 from ligandin for glucuronidation.
authors.affiliation: Department of Applied Biological Science, Tokyo University of Science, Chiba, Japan.
authors.forename: Emi
authors.initials: E
authors.lastname: Akizawa
authors.forename: Kotaro
authors.initials: K
authors.lastname: Koiwai
authors.forename: Takahide
authors.initials: T
authors.lastname: Hayano
authors.forename: So
authors.initials: S
authors.lastname: Maezawa
authors.forename: Toyofumi
authors.initials: T
authors.lastname: Matsushita
authors.forename: Osamu
authors.initials: O
authors.lastname: Koiwai