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METABOLISM OF PHOSPHATIDYLCHOLINE, PHOSPHATIDYLINOSITOL AND PALMITYL CARNITINE IN SYNAPTOSOMES FROM RAT BRAIN 1
Author(s) -
AbdelLatif A. A.,
Roberts M. B.,
Karp W. B.,
Smith J. P.
Publication year - 1973
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1973.tb12116.x
Subject(s) - phosphatidylinositol , microsome , phosphatidylcholine , inositol , synaptosome , biochemistry , phospholipid , carnitine , mitochondrion , chemistry , transferase , choline , diglyceride , enzyme , membrane , receptor , kinase
— Synthesis of phosphatidylcholine, phosphatidylinositol and palmityl carnitine in synaptosomes isolated from rat brain was investigated and compared with the synthesis of these compounds in microsomes and mitochondria. Electron microscopic and marker enzyme studies showed the contaminants in the synaptosomal preparation to consist of a few microsomes and almost no free mitochondria. In synaptosomes, addition of 1,2‐diglyceride exerted no effect on the incorporation of [ 14 C]choline into phosphatidylcholine or on the incorporation of [ 3 H]myo‐inositol into phosphatidylinositol, but it stimulated the incorporation of CDP[1,2‐ 14 C]choline into phosphatidylcholine by more than 50 per cent. The incorporation of the latter in intact synaptosomes, lysed synaptosomes and purified mitochondria was 15‐6, 27 and 9‐9 per cent, respectively, of that in the microsomes. The incorporation of [ 3 H]myo‐inositol into the phosphatidylinositol of synaptosomes and purified mitochondria was 15‐8 and 11‐1 per cent, respectively, of that in the microsomes. Maximal incorporation of [ 3 H]myo‐inositol occurred at pH 7–5 in a medium containing Mg 2+ and CTP; it was linear with time and protein concentration and was inhibited by 1 mM Ca 2 + but unaffected by the presence of ATP. This incorporation of myo‐inositol appeared to occur through the reversal of the CDP‐diglyceride: inositol transferase reaction. The demonstration of carnitine palmityl transferase in synaptosomes indicated that, as in mitochondrial and erythrocyte membranes, fatty acids can be transported across the synaptosomal membrane. In contrast to mitochondria where maximal incorporation of [ 14 C]carnitine into palmityl carnitine was observed after 20 min of incubation, the incorporation in synaptosomes increased as a function of time up to 60 min of incubation. We conclude that synaptosomes can carry on de novo synthesis of lipids, although at a limited rate. From the present data we cannot state with certainty how much of this synthesis is attributable to membranes originating from the endoplasmic reticulum.