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- W8787002 abstract "The supply of choline (Ch) to the brain has been discussed by Ansell, G.B. and Spanner, S. (in Cholinergic Mechanisms and Psychopharmacology, D. Jenden, Ed., Plenum Press, New York, pp. 431–445). These authors reviewed evidence for the loss of Ch from the brain and its replacement by Ch from the phospholipids. Estimations of free Ch in the brain vary but may be as low as 8.7 nmol · g−1 (Mann, S.P. and Hebb, C., J. Neurochem., 28, 241–244, 1977). The enzymes capable of releasing Ch from phospholipids and their metabolites may be of importance with regard to the supply of choline for the synthesis of acetylcholine (ACh). Two of these enzymes have now been examined. The presence of glycerophospho-phorylcholine diesterase and its distribution in the brain has already been reported (Mann, S.P., Experientia, 31, 1256–1258, 1975). The base-exchange system (Porcellati, G., et al., J. Neurochem. 18, 1395–1417, 1971) and alkaline phosphatase have now been investigated in the brain of the rats. The base-exchange system was found to be stimulated by Ca2+ and to have an activity of 2.1 nmol · g−1 · h−1 for both incorporation and release of Ch from phospholipids at pH 9.0. The system was evenly distributed in all fractions obtained by subcellular fractionation of the cerebrum. Ch incorporation and release were both inhibited by hemicholinium-3 (HC-3). Phospholipase D from plants was examined and had an optimum pH of 5.6; HC-3 did not inhibit this enzyme. Alkaline phosphatase activity was assayed radiometrically and was found in all brain regions; the highest activity (38 μmol · g−1 · h−1 was in the cerebrum at an optimum pH of 9.0. The enzyme had a Km for choline phosphate of 1.06 mM. Subcellular fractionation showed high concentrations in fractions P2 and P3 (29 and 31%); 47% of the activity in P2 was found in the synaptosome-rich (B) fraction. Activity was also found in fractions D (vesicles, 12%), F, G, H (synaptosome ghosts, 19, 14 and 27%) and I (mitrochondria, 8%), obtained after osmotic rupture of the P2 fraction. These results indicate that there exist, within the brain, enzymes capable of making good the loss of Ch from the brain by releasing Ch from phospholipids and their metabolites. Ultimately, therefore, the Ch used in ACh synthesis may originate from the phospholipids of the brain." @default.
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- W8787002 date "1979-01-01" @default.
- W8787002 modified "2023-09-28" @default.
- W8787002 title "Source of Choline for Acetylcholine Synthesis in the Brain" @default.
- W8787002 doi "https://doi.org/10.1016/s0079-6123(08)64682-8" @default.
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