Membrane Lipid Composition and Vesicle Size Modulate Bilirubin Intermembrane Transfer EVIDENCE FOR MEMBRANE-DIRECTED TRAFFICKING OF BILIRUBIN IN THE HEPATOCYTE*

摘要: To characterize the mechanisms underlying intracellular bilirubin transport, stopped-flow fluorometry was utilized to study effects of membrane vesicle size and lipid composition on kinetics unconjugated movement between model native hepatocyte membranes. Bilirubin transfer rates declined asymptotically with increasing donor diameter, due primarily a 1.4 kcal.mol-1 decrease in entropy activation for larger vesicles. The incorporation phosphatidylethanolamine phosphatidylserine significantly enhanced dissociation from phosphatidylcholine Cholesterol induced biphasic effect rate constant; an initial 248 217 s-1 associated cholesterol:phospholipid ratios up 20% followed by dramatic rise 312 as cholesterol concentration increased 70 mol %. isolated rat liver endoplasmic reticulum (9.1 s-1) slower than both basolateral canalicular plasma membranes, which exhibited constants 11.7 25.8 s-1, respectively. Collectively, these data suggest that cholesterol: phospholipid ratio is principal determinant We postulate inherent cellular gradient creates directed flux teh represents potential driving force transport.