Document Detail

In vitro evidence that phospholipid secretion into bile may be coordinated intracellularly by the combined actions of bile salts and the specific phosphatidylcholine transfer protein of liver.
MedLine Citation:
PMID:  8061007     Owner:  NLM     Status:  MEDLINE    
Using model systems, we explored a potential function of hepatic phosphatidylcholine transfer protein to extract biliary-type phosphatidylcholines from intracellular membranes (e.g., smooth endoplasmic reticulum) and deliver them to canalicular plasma membranes where biliary secretion occurs. We measured transfer rates of parinaroyl phosphatidylcholine, a naturally fluorescent phospholipid, from small unilamellar vesicles composed of sn-1 palmitoyl, sn-2 parinaroyl phosphatidylcholine, and egg yolk phosphatidylcholine (molar ratio 75:25) wherein the fluorophore is self-quenched to small unilamellar vesicles composed of phosphatidylethanolamine, sphingomyelin, phosphatidylserine, phosphatidylinositol, and cholesterol (molar ratios 22:22:10:8:38) representing model microsomal and canalicular plasma membranes, respectively. Following addition of phosphatidylcholine transfer protein (purified from bovine liver), fluorescence intensity increased exponentially indicating net phosphatidylcholine transfer from donor to acceptor vesicles. Submicellar concentrations of a wide hydrophobicity range of common and uncommon taurine and glycine conjugated bile salts species (anionic steroid detergent-like molecules), sodium taurofusidate (a conjugated fungal bile salt analog), and sodium dodecyl sulfate and octylglucoside, anionic and nonionic straight chain detergents, respectively, markedly stimulated phosphatidylcholine transfer protein activity. This 40-115-fold effect was most pronounced for the common bile salts and correlated positively with bile salt hydrophobicity. Thermodynamic analysis of net transfer revealed that the rate-limiting step was extraction of phosphatidylcholine molecules from donor vesicles and that bile salts facilitated their capture by enhancing both phosphatidylcholine transfer protein binding as well as perturbing phospholipid packing in vesicle bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)
D E Cohen; M R Leonard; M C Carey
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  33     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1994 Aug 
Date Detail:
Created Date:  1994-09-21     Completed Date:  1994-09-21     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  9975-80     Citation Subset:  IM    
Department of Medicine, Harvard Medical School, Boston, Massachusetts.
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MeSH Terms
Androgen-Binding Protein*
Bile / metabolism*
Bile Acids and Salts / pharmacology*
Bile Canaliculi / ultrastructure
Carrier Proteins / metabolism*
Detergents / pharmacology
Intracellular Membranes / metabolism
Liposomes / metabolism
Liver / metabolism*,  ultrastructure
Microsomes / ultrastructure
Phosphatidylcholines / metabolism
Phospholipid Transfer Proteins
Phospholipids / secretion*
Grant Support
Reg. No./Substance:
0/Androgen-Binding Protein; 0/Bile Acids and Salts; 0/Carrier Proteins; 0/Detergents; 0/Liposomes; 0/Phosphatidylcholines; 0/Phospholipid Transfer Proteins; 0/Phospholipids; 107-35-7/Taurine; 56-40-6/Glycine

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