Activity of phospholipid-synthesizing enzymes in rat liver plasma membranes and the source of biliary lecithin |
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Authors: | I M Yousef M M Fisher J Piekarski B J Holub |
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Affiliation: | (1) Departments of Pathology and Medicine, University of Toronto, Toronto, Ontario, Canada;(2) Department of Nutrition, University of Guelph, Guelph, Ontario, Canada;(3) Present address: Canadian Hepatic Foundation, Toronto, Ontario, Canada |
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Abstract: | The potential for the synthesis of phosphatidylcholine by the bile canalicular membrane of the liver cell was assessed by
measuring the activity of a number of phospholipid synthesizing enzymes in isolated bile canalicular membrane fractions from
rat liver. The activity of these various enzymes was compared to that present in noncanalicular liver cell plasma membranes
and in microsomes. The CDP-choline: 1,2-diacyl-sn-glycerol-cholinephosphotransferase was virtually absent from the bile canalicular membranes but the specific activities of
S-adenosyl-L-methionine:phosphatidylethanolamine N-methyltransferase and acyl-CoA:1-acyl-sn-glycero-3-phosphoryl-choline acyltransferase were 11–15% of those found in the microsomes. The bile canalicular membranes
also contained detectable acyl-CoA:sn-glycero-3-phosphate acyltransferase activity and the ability to potentiate the Ca++-stimulated exchange of bases between different phospholipids. These findings indicate that the bile canalicular membranes
have a very limited capacity for the formation of phosphatidylcholine under the assay conditions employed.
A preliminary report of this paper was given at the AOCS Spring Meeting, Dallas, April 1975. |
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