Phospholipid Methylase Activity, [3H]S-Adenosyl-l-Homocysteine Binding, and S-Adenosyl-l-Methionine and S-Adenosyl-l-Homocysteine Levels in Rat Brain During Maturation

The changes in activity of phospholipid methyltransferase I and [3H]S-adenosyl-L-homocysteine ([3H]SAH) binding were determined in cortical membrane preparations from newborn rats and rats 1, 2, and 8 months old. The activity of phospholipid methyltransferase I and the [3H]SAH binding were significantly greater (respectively, +30 and +40%) in newborn rats than in 1-, 2-, and 8-month-old rats. The methylated products at days 1 and 30 were identical. These changes in methyltransferase activity may be correlated with variations in concentration of S-adenosyl-L-methionine (SAM) and SAH. The endogenous SAM level was higher and the SAH level was lower in newborn compared with adult rats. These data suggested that the processes of methylation were favored in newborn rats. The modifications observed after treatment with L-homocysteine reinforced this hypothesis.     

The Regional Concentrations of S-Adenosyl-l-Methionine, S-Adenosyl-l-Homocysteine, and Adenosine in Rat Brain

Abstract: The concentrations of S -adenosyl- l -methionine (SAM), S -adenosyl- l -homocysteine (SAH), and adenosine (Ado) were determined in whole brain and rat brain regions by HPLC. The whole brain contains, respectively, 22 nmol, 1 nmol, and 64 nmol of SAM, SAH, and Ado per g of wet tissue. Their distribution indicated that SAM and SAH levels are highest in brainstem, whereas the Ado level is highest in cortex. With aging the SAM concentrations decrease in whole brain, brainstem, and hypothalamus (–25%) and SAH levels increase by 90% in striatum and by 160% in cerebellum, while Ado levels are increased in all regions by 100–180%.     

Phospholipid Methylation and Noradrenaline Exchanges in a Synaptosomal Preparation from the Rat Brain

Abstract: When synaptosomes from rat brain were incubated with S -adenosylmethionine (10⁻³ M ), noradrenaline uptake and KCI-stimulated release were decreased. These effects were dependent on MgCl₂, temperature, and incubation time. We have investigated the enzymatic methylation of phosphatidylethanolamine to give phosphatidylcholine.     

In Vivo Elevation of Mouse Brain S-Adenosyl-L-Homocysteine after Treatment with L-Homocysteine

Intraperitoneal coadministration of adenosine and L-homocysteine markedly increased S-adenosyl-L-homocysteine in whole mouse brain, but further investigations showed that this elevation could also be produced following administration of L-homocysteine alone. The noted increase was maximal (+1325%) 10 min after treatment, remaining at about this level for 30-40 min before returning to control values after 180 min. Cerebral adenosine levels were decreased after treatment with L-homocysteine, adenosine, or these two substances in combination.     

Properties of Particulate and Detergent-Solubilized Phospholipid N-Methyltransferase Activity from Calf Brain

Abstract: Calf brain membranes catalyze the enzymatic transfer of [CH₃-³H]methyl groups from S-adenosyl-l -[CH₃-³H]methionine into endogenous phosphatidyl-N-methylethanolamine (PME), phosphatidyl-N,N-dimethylethanolamine (PDE), and phosphatidylcholine (PC). Phospholipid N-methylation can be stimulated by the addition of exogenous PME or PDE, added in aqueous dispersions with sodium taurocholate. When membranes are incubated in the presence of exogenous PME, [CH₃-³H]PDE represents 86% of the labeled phospholipid products. When exogenous PME is replaced by PDE, 91% of the label is incorporated into PC. Thus, under these in vitro conditions it is possible to assay PME- and PDE-N-methyitransferase activity separately. The calf brain phospholipid N-methyltransferase activity has also been solubilized by treating the membranes ultrasonically in the presence of Triton X-100 and 10 mM monothioglycerol. When the detergent extracts are incubated in the presence of exogenous PME, [CH₃-³H]PDE represents 86% of the enzymatically labeled products. In the presence of exogenous PDE, more than 97% of the label is incorporated into PC. Optimal conditions for the membrane-bound and detergent-solubilized PME- and PDE-N-methyltransferase activity have been established. These conditions have been used as a basis for testing the hypothesis that the conversion of PME to PC is catalyzed by a single enzyme in calf brain. In these studies, PME- and PDE-N-methyltransferase activities have been found to be similar, if not identical, with respect to: (1) extractability with Triton X-100; (2) pH optimum; (3) response to divalent cations; (4) apparent K_m, for S-adenosyl-l -methionine and K_I for S-adenosyl-l -homocysteine, (5) sensitivity to N-ethylmaleimide; and (6) thermal inactivation at 55°. Overall, these results are consistent with the conclusion that in calf brain, PME and PDE are methylated by the same enzyme or by two phospholipid N-methyltransferases having very similar properties.     

Protective role of S-adenosyl-l-methionine against hydrochloric acid stress in Saccharomyces cerevisiae

S-adenosyl-l-methionine (AdoMet, 1 mM) protects the stationary phase cells of Saccharomyces cerevisiae against the killing effect of acid (10 mM HCl, pH ∼ 2). Both the acid and the acid plus AdoMet treatment for 2 h increased the plasma membrane H⁺-ATPase activity; thereafter it decreased to the basal level. AdoMet partially recovered the intracellular pH (pH_in) that dropped in presence of acid. AdoMet treatment facilitated acid induced phospholipid biosynthesis as well as membrane proliferation, which was reflected in the cellular lipid composition.     

Regional Distribution of Methionine Adenosyltransferase in Rat Brain as Measured by a Rapid Radiochemical Method

Abstract: The distribution of methionine adenosyltransferase (MAT) in the CNS of the rat was studied by use of a rapid, sensitive and specific radiochemical method. The S -adenosyl-[methyl-¹⁴C] l -methionine ([¹⁴C]SAM) generated by adenosyl transfer from ATP to [methyl-¹⁴C] l -methionine is quantitated by use of a SAM-consuming transmethylation reaction. Catechol O -methyltransferase (COMT), prepared from rat liver, transfers the methyl-¹⁴C group of SAM to 3,4-dihydroxybenzoic acid. The ¹⁴C-labelled methylation products, vanillic acid and isovanillic acid, are separated from unreacted methionine by solvent extraction and quantitated by liquid scintillation counting. Compared to other methods of MAT determination, which include separation of generated SAM from methionine by ion-exchange chromatography, the assay described exhibited the same high degree of specificity and sensitivity but proved to be less time consuming. MAT activity was found to be uniformly distributed between various brain regions and the pituitary gland of adult male rats. In the pineal gland the enzyme activity is about tenfold higher.