title: Role of the physical state of the hepatic microsomal membrane in the formation of bilirubin diglucuronide.
abstract: In vitro formation of bilirubin diglucuronide by rat hepatic microsomes proceeds efficiently only under specific conditions; i.e., a low level of bilirubin, temperature greater than 23-24 degrees C and treatment of the microsomes with a very specific level of perturbant (J. Biol. Chem., 258: 15028-15036). In the present study, the effect of temperature and detergents on the anisotropy of fluorescent probes in the rat hepatic microsomal membrane was used to determine the role of the physical state of the membrane in controlling the formation of bilirubin diglucuronide. A lipid phase separation that occurred at 23 +/- 2 degrees C was identified in these membranes indicating that bilirubin diglucuronide is formed efficiently only above the lipid phase separation when the phospholipids are in the liquid crystalline state. In addition, use of fluorescent probes for the surface and core of the membrane indicates that alterations in the physical state of the hydrophobic core rather than the phospholipid polar head group region of the membrane controls the in vitro formation of bilirubin diglucuronide.
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000031:analogs & derivatives* / Q000096:biosynthesis; D003902:Detergents / Q000494:pharmacology; D005454:Fluorescence Polarization; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature
chemical_list: D003902:Detergents; D008563:Membrane Lipids; C019270:bilirubin diglucuronide; D001663:Bilirubin