The phospholipid-dependence of uridine diphosphate glucuronyltransferase. Temperature-dependence of microsomal enzyme activity and thermotropic changes in membrane structure.
Arrhenius plots of the non-latent UDP-glucuronyltransferase (p-nitrophenol acceptor) activity of guinea-pig microsomal membranes prepared with 154 mM-KCl were linear from 5 to 40 degrees C. Arrhenius plots for other microsomal preparations from guinea pig and rat liver that show various degrees of transferase latency, exhibited two linear regions intersecting at a sharp transition point near 20-25 degrees C. This discontinuity was abolished or greatly decreased when transferase latency was removed by treating the membranes with perturbants of phospholipid bilayer strucutre. The fluorescent probe N-phenyl-1-naphthyl-amine detected a thermotropic change in the fluidity of the phospholipid acyl chains of all the microsomal membrane preparations studied, at temperatures close to those of the Arrhenius-plot transitions. It is concluded that the thermotropic change in the structure of the membrane bilayer probably is a 'phase separation' or clustering of phospholipids, which affects a permeability barrier that restricts access of substrate to the transferase molecules.
D000818:Animals; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000187:drug effects / Q000201:enzymology; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010740:Phospholipases / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D013050:Spectrometry, Fluorescence; D013696:Temperature
D010743:Phospholipids; D011092:Polyethylene Glycols; D014453:Glucuronosyltransferase; D010740:Phospholipases