title: Protein-lipid interactions in human small intestinal brush-border membranes.
abstract: Brush-border membranes prepared from proximal and distal human small intestine were characterized with respect to lipid fluidity, lipid composition, and protein-lipid interactions. Steady-state fluorescence polarization and differential polarized phase fluorometry revealed that the "static" and "dynamic" rotational components of fluidity (assessed by r infinity values of 1,6-diphenyl-1,3,5-hexatriene and r values of 12-anthroylstearate, respectively) were greater in the distal membranes compared with their proximal counterparts. The lipid fluidity of distal brush-border membranes was also greater as measured by excimer/monomer fluorescence ratio intensities of pyrene decanoate. A lower molar ratio of cholesterol/phospholipid in the distal membranes was responsible for these regional fluidity differences. Lipid thermotropic transitions were detected at 26-28 degrees C using 1,6-diphenyl-1,3,5-hexatriene in proximal and distal membranes. Arrhenius plots of p-nitrophenylphosphatase and gamma-glutamyl transpeptidase activities demonstrated breakpoints in the vicinity of the lipid thermotropic transition temperatures (28-30 degrees C), whereas maltase and sucrase yielded a single activity slope over the range of 10-40 degrees C. Moreover, 50 mM benzyl alcohol fluidized proximal brush-border membranes and increased p-nitrophenylphosphatase activity in this membrane. This agent also shifted the phase transition temperature of the membrane and breakpoint temperature of this enzymatic activity from approximately 28 degrees C to 19 degrees C. These findings demonstrate that differences in human small intestinal brush-border membrane lipid fluidity and lipid composition exist between proximal and distal regions of this organ. Furthermore, alterations in fluidity and/or lipid composition modulate p-nitrophenylphosphatase and gamma-glutamyl transpeptidase but not sucrase or maltase activities in these membranes.
authors.affiliation: Department of Medicine, University of Chicago Pritzker School of Medicine, Illinois 60637.
authors.forename: P K
authors.initials: PK
authors.lastname: Dudeja
authors.forename: J M
authors.initials: JM
authors.lastname: Harig
authors.forename: K
authors.initials: K
authors.lastname: Ramaswamy
authors.forename: T A
authors.initials: TA
authors.lastname: Brasitus
mesh_terms: D000293:Adolescent; D000328:Adult; D019905:Benzyl Alcohol; D001592:Benzyl Alcohols / Q000494:pharmacology; D004161:Diphenylhexatriene; D004347:Drug Interactions; D005453:Fluorescence; D006801:Humans; D007421:Intestine, Small / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D050356:Lipid Metabolism; D008297:Male; D008871:Microvilli / Q000201:enzymology / Q000378:metabolism; D008875:Middle Aged; D011506:Proteins / Q000378:metabolism*; D013696:Temperature
chemical_list: D001592:Benzyl Alcohols; D011506:Proteins; D004161:Diphenylhexatriene; D019905:Benzyl Alcohol