PubMed · 574314
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L Pauling. 1979-10-26. Treating mental disorders.. https://doi.org/10.1126/science.574314-a
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In yeast, as in other eukaryotes, phosphatidylcholine (PC) can be synthesized via methylation of phosphatidylethanolamine or from free choline via the CDP-choline pathway. In yeast, PC biosynthesis is required for the repression of the phospholipid biosynthetic genes, including the INO1 gene, in response to inositol. In this study, we analyzed the effect of mutations in genes encoding enzymes involved in PC biosynthesis on the transcriptional regulation of phospholipid biosynthetic genes. We report that repression of INO1 transcription in response to inositol is clearly dependent on ongoing PC biosynthesis, but it is independent of the route of synthesis. Our results also suggest that intermediates in the phosphatidylethanolamine methylation and CDP-choline pathways are not responsible for generating the regulatory signal that results in repression of INO1 and other coregulated genes of phospholipid biosynthesis. Furthermore, repression of INO1 is not tightly correlated to the proportion of PC in the total cellular phospholipids. Rather, we report that when the rate of synthesis of PC becomes growth limiting, the addition of inositol fails to repress the phospholipid biosynthetic genes, but when the rate of PC synthesis is sufficient to sustain normal growth, the addition of inositol to the growth medium has the effect of repressing INO1 and other phospholipid biosynthetic genes.
Liposomes with mean diameters between 45 and 73 nm have been prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at pH 8.0; and a new methodology is described which allows one to quantitatively follow the phospholipase D-catalyzed transformation of POPC to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidic acid and free choline. The method does not require a special sample preparation; it takes advantage of the fact that the chemical shift of the protons of the three methyl groups in free choline differs from the chemical shift of the choline methyl protons in POPC. Measurements have been carried out under different experimental configurations and they have been paralleled by electron and light microscopy studies, partially using a fluorescently labeled phospholipid. It has been found that for a fixed concentration of the Ca2+-independent phospholipase D from Streptomyces sp. AA 586 the initial velocity and the reaction yields depend on the size of the vesicles. The smaller the vesicles, the higher the yields and the lower the initial rates. Furthermore, the size of the liposomes does not change during hydrolysis of the external POPC layer.
Choline is a primary degradation product of succinylcholine chloride. Determination of low concentration choline in succinylcholine chloride bulk drug and formulation is a challenge, due to the lack of sensitive detection methods. A reversed-phase separation method with postcolumn suppression conductivity detection is described for the determination of choline. Hexanesulfonic acid is employed as an ion-pair reagent in the mobile phase, which allows the accomplishment of both reversed-phase separation and a sensitive conductivity detection. Detection sensitivity is significantly enhanced by passing the mobile phase through a postcolumn cation suppressor, where hexanesulfonic acid is removed and the background conductance is reduced. This method is simple and sensitive. No sample derivatization procedure is required. The detection limit for choline is about 10 pmol.