The roles of phospholipase D and a GTP-binding protein in guanosine 5'-[gamma-thio]triphosphate-stimulated hydrolysis of phosphatidylcholine in rat liver plasma membranes. |
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| Authors: | K M Hurst B P Hughes and G J Barritt |
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| Affiliation: | Department of Medical Biochemistry, School of Medicine, Flinders University of South Australia, Adelaide. |
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| Abstract: | 1. Guanosine 5'-gamma-thio]triphosphate (GTPS]) stimulated by 50% the rate of release of 3H]choline and 3H]phosphorylcholine in rat liver plasma membranes labelled with 3H]choline. About 70% of the radioactivity released in the presence of GTPS] was 3H]choline and 30% was 3H]phosphorylcholine. 2. The hydrolysis of phosphorylcholine to choline and the conversion of choline to phosphorylcholine did not contribute to the formation of 3H]choline and 3H]phosphorylcholine respectively. 3. The release of 3H]choline from membranes was inhibited by low concentrations of SDS or Triton X-100. Considerably higher concentrations of the detergents were required to inhibit the release of 3H]phosphorylcholine. 4. Guanosine 5'-beta gamma-imido]triphosphate and guanosine 5'-alpha beta-methylene]triphosphate, but not adenosine 5'-gamma-thio]-triphosphate, stimulated 3H]choline release to the same extent as did GTPS]. The GTPS]-stimulated 3H]choline release was inhibited by guanosine 5'-beta-thio]diphosphate, GDP and GTP but not by GMP. 5. It is concluded that, in rat liver plasma membranes, (a) GTPS]-stimulated hydrolysis of phosphatidylcholine is catalysed predominantly by phospholipase D with some contribution from phospholipase C, and (b) the stimulation of phosphatidylcholine hydrolysis by GTPs] occurs via a GTP-binding regulatory protein. |
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