Phosphatidylinositol exchange protein. Effects of membrane structure on activity and evidence for a ping-pong mechanism. |
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Authors: | G M Helmkamp K W Wirtz L L van Deenen |
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Institution: | Laboratory of Biochemistry, State University of Utrecht, Transitorium 3, Universiteitscentrum “De Uithof,” Padualaan 8, Utrecht, The Netherlands |
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Abstract: | Phosphatidylinositol exchange protein, purified from bovine cerebral cortex, catalyzes the transfer of phosphatidylinositol and, to a lesser extent, phosphatidylcholine between rat liver microsomes and egg phosphatidylcholine liposomes. Transfer activity is sensitive to pH, temperature, and the method of liposome preparation. Variation of the phospholipid composition of the liposomes produces vesicles for which the apparent Michaelis constant decreases with increasing molar proportions of phosphatidylinositol. Interaction of exchange protein with liposomes containing radioactively labeled phosphatidylcholine allows the isolation of a phospholipid-protein complex; dissociation of this complex occurs upon subsequent interaction with unlabeled liposomes. Changes in the concentration of the two membrane species, microsomes and liposomes, yield results which are interpreted in terms of a ping-pong kinetic mechanism for the protein-catalyzed, intermembrane transfer of phospholipids. |
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Keywords: | Recipient of National Institutes of Health Fellowship No FO2-HL53820 from the National Heart and Lung Institute Present address and address for reprints: Department of Biochemistry University of Kansas Medical Center Kansas City Kan 66103 |
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