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1.
The role of methionine as a precursor in mugineic acid (MA) biosynthesis was studied by feeding 15 N-ammonium sulfate, 14 C-amino acids, and [1-14 C, 15 N]-methionine to iron-deficient barley roots ( Hordeum vulgare L. cv. Minorimugi), grown hydroponically. The incorporation of isotopes into amino acids was also examined. Methionine appears to be the most efficient precursor of the mugineic acid family (MAs) of phytosiderophores; homoserine was also incorporated into the MAs, but other amino acids such as glutamate, alanine, and γ-amino butyric acid did not act as precursors of MAs. Carbon-14 and 15 N of methionine were incorporated into MAs. This specific incorporation of 14 C and 15 N indicated that the nitrogen atoms of MAs were derived from two molecules of methionine. It is suggested that deoxymugineic acid (DMA) is probably the first phytosiderophore to be synthesized on the biosynthetic pathway of MAs. 相似文献
2.
Abstract: The recycling of methionine via homocysteine was measured in vivo in brain. After constant intravenous infusions (5 h) of both [3 H-methyl] methionine and [35 S]methionine into rats, the ratios of [3 H-methyl]methionine to [35 S]methionine in liver, brain and plasma were determined, Similar experiments were performed in rabbits, except that the [3 H-methyl]- and [3 S]methionine were injected intraventricularly. If the methyl group of methionine was removed with the formation of homocysteine and then replaced by another (unlabeled) methyl group, the specific activity of the [3 H-methyl]methionine would decrease more than that of [35 S]methionine; i.e., the ratio of [3 H-methyl]- to [35 S]methionine in the tissue would decline. The results showed that the ratios of [3 H-methyl]- to [35 S]methionine in liver and brain were less than the same ratio in plasma in the rats. The comparable ratios in the brain and CSF of rabbits were less than the ratio in the injectate. Since brain contains only one enzyme capable of remethylating homocysteine to methionine, the vitamin B-12–dependent methyltetrahydrofolate-homocysteine methyltransferase (EC 2.1.1.13), our results for methionine recycling via homocysteine in brain strongly support the activity of this enzyme in brain in vivo. 相似文献
3.
Biosynthesis of Polyamines in Mouse Brain: Effects of Methionine Sulfoximine and Adenosylhomocysteine 总被引:1,自引:1,他引:0
Raffaele Porta Robert A. Schatz Stephen B. Tatter Otto Z. Sellinger 《Journal of neurochemistry》1983,40(3):836-841
Abstract: This study examines the consequences on cerebral polyamine biosynthesis of increases and decreases in cerebral methylation. Increases were elicited by administering the convulsant agent methionine sulfoximine (MSO) and decreases by elevating in vivo the cerebral levels of the methylation inhibitor S -adenosyl-homocysteine. Following the intraventricular (i.vt.) administration of one of the two possible polyamine precursors, [1,4-14 C]putrescine, the specific radioactivity (sra) of the newly formed [14 C]spermidine remained unchanged. Conversely, after i.vt. l -[3,4-14 C]methionine, the other polyamine precursor, significantly higher sra values for [14 C]spermidine and [14 C]spermine were recorded in the brains of the MSO-treated animals. [14 C] S - adenosylmethionine in the brain of the MSO-treated animals was also more highly labeled following [1-14 C]-methionine, indicating its accelerated formation relative to controls. We also investigated the effect of the administration of adenosine + homocysteine, a treatment that results in elevated brain adenosylhomocysteine levels, on polyamine biosynthesis from [3,4-14 C]-methionine. The results of these experiments show both significantly lower sra values for [14 C]spermidine and [14 C]spermine and significantly higher than control endogenous methionine levels, a clear sign of the existence of a retardation in the conversion of methionine to polyamines under these conditions. In conclusion, the present study demonstrates that while interference with cerebral methylation results in significant alterations of the rate of formation of the methionine moiety of spermidine and spermine, it has no effect on the entry of the putrescine moiety into the two polyamine molecules. 相似文献
4.
We examined the biosynthesis of trigonelline in leaves and fruits of Arabica coffee ( Coffea arabica ) plants. [3 H]Quinolinic acid, which is an intermediate of de novo pyridine nucleotide synthesis, and [14 C]nicotinamide and [14 C]nicotinic acid, which are degradation products of NAD, were converted to trigonelline and pyridine nucleotides. These tracer experiments suggest that the pyridine nucleotide cycle, nicotinamide → nicotinic acid → nicotinic acid mononucleotide (NaMN) → nicotinic acid adenine dinucleotide (NaAD) → NAD → nicotinamide mononucleotide (NMN) → nicotinamide, operates in coffee plants, and trigonelline is synthesized from nicotinic acid formed in the cycle. Trigonelline accumulated up to 18 µmol per leaf in developed young leaves, and then decreased with age. Although the biosynthetic activity of trigonelline from exogenously supplied [14 C]nicotinamide was observed in aged leaves, the endogenous supply of nicotinamide may be limited, reducing the contents in these leaves. Trigonelline is synthesized and accumulated in fruits during development. The trigonelline synthesis in pericarps is much higher than that in seeds, but its content in seeds is higher than pericaps, so that some of the trigonelline synthesized in the pericarps may be transported to seeds. Trigonelline in seeds may be utilized during germination, as its content decreases. Trigonelline synthesis from [14 C]nicotinamide was also found in Theobroma cacao plants, but instead of trigonelline, nicotinic acid-glucoside was synthesized from [14 C]nicotinamide in Camellia sinensis plants. 相似文献
5.
Ranocha P McNeil SD Ziemak MJ Li C Tarczynski MC Hanson AD 《The Plant journal : for cell and molecular biology》2001,25(5):575-584
Angiosperms synthesize S-methylmethionine (SMM) from methionine (Met) and S-adenosylmethionine (AdoMet) in a unique reaction catalyzed by Met S-methyltransferase (MMT). SMM serves as methyl donor for Met synthesis from homocysteine, catalyzed by homocysteine S-methyltransferase (HMT). MMT and HMT together have been proposed to constitute a futile SMM cycle that stops the free Met pool from being depleted by an overshoot in AdoMet synthesis. Arabidopsis and maize have one MMT gene, and at least three HMT genes that belong to two anciently diverged classes and encode enzymes with distinct properties and expression patterns. SMM, and presumably its cycle, must therefore have originated before dicot and monocot lineages separated. Arabidopsis leaves, roots and developing seeds all express MMT and HMTs, and can metabolize [35S]Met to [35S]SMM and vice versa. The SMM cycle therefore operates throughout the plant. This appears to be a general feature of angiosperms, as digital gene expression profiles show that MMT and HMT are co-expressed in leaves, roots and reproductive tissues of maize and other species. An in silico model of the SMM cycle in mature Arabidopsis leaves was developed from radiotracer kinetic measurements and pool size data. This model indicates that the SMM cycle consumes half the AdoMet produced, and suggests that the cycle serves to stop accumulation of AdoMet, rather than to prevent depletion of free Met. Because plants lack the negative feedback loops that regulate AdoMet pool size in other eukaryotes, the SMM cycle may be the main mechanism whereby plants achieve short-term control of AdoMet level. 相似文献
6.
Elevated pyruvate,orthophosphate dikinase (PPDK) activity alters carbon metabolism in C3 transgenic potatoes with a C4 maize PPDK gene 总被引:1,自引:0,他引:1
Ken Ishimaru Yasunobu Ohkawa Teruo Ishige Dennis J. Tobias Ryu Ohsugi 《Physiologia plantarum》1998,103(3):340-346
Changes in carbon metabolism and δ13 C value of transgenic potato plants with a maize pyruvate,orthophosphate dikinase (PPDK; EC 2.7.9.1) gene are reported. PPDK catalyzes the formation of phospho enol pyruvate (PEP), the initial acceptor of CO2 in the C4 photosynthetic pathway. PPDK activities in the leases of transgenic potatoes were up to 5.4‐fold higher than those of control potato plants (wild‐type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r2 = 0.81), and was positively correlated with malate content (r2 = 0.88). A significant increase in the δ13 C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO2 . These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C4 ‐type carbon metabolism. However, since parameters associated with CO2 gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants. 相似文献
7.
M. DURANCEAU J. GHASHGHAIE F. BADECK E. DELEENS & G. CORNIC 《Plant, cell & environment》1999,22(5):515-523
The variations in δ 13 C in both leaf carbohydrates (starch and sucrose) and CO2 respired in the dark from the cotyledonary leaves of Phaseolus vulgaris L. were investigated during a progressive drought. As expected, sucrose and starch became heavier (enriched in 13 C) with decreasing stomatal conductance and decreasing p i / p a during the first half (15 d) of the dehydration cycle. Thereafter, when stomata remained closed and leaf net photosynthesis was near zero, the tendency was reversed: the carbohydrates became lighter (depleted in 13 C). This may be explained by increased p i / p a but other possible explanations are also discussed. Interestingly, the variations in δ 13 C of CO2 respired in the dark were correlated with those of sucrose for both well-watered and dehydrated plants. A linear relationship was obtained between δ 13 C of CO2 respired in the dark and sucrose, respired CO2 always being enriched in 13 C compared with sucrose by ≈ 6‰. The whole leaf organic matter was depleted in 13 C compared with leaf carbohydrates by at least 1‰. These results suggest that: (i) a discrimination by ≈ 6‰ occurs during dark respiration processes releasing 13 C-enriched CO2 ; and that (ii) this leads to 13 C depletion in the remaining leaf material. 相似文献
8.
Mary J. Wilson Nina V. Myasishcheva Gary D. Stoner Lionel A. Poirier 《In vitro cellular & developmental biology. Plant》1983,19(2):134-140
Summary The enzymeN
5-methyltetrahydrofolate: homocysteine methyltransferase (methionine synthetase) catalyzes the synthesis of methionine from
homocysteine. Methylcobalamin is a cofactor for the reaction. The effects of methionine deprivation and methylcobalamin supplementation
on the growth of normal and transformed rat liver epithelial cell lines were determined using growth constants to quantitate
cell proliferation. No marked specific requirement by the transformed cell lines for methionine relative to leucine was observed.
A sigmoidal relationship, however, was found to exist between growth constants and the logarithms of the amino acid concentrations
for both normal and transformed cells. Methylcobalamin stimulated the growth rates of the normal and transformed liver cells
in methionine-deficient, homocysteine-containing medium. Growth on methionine was not increased by the addition of methylcobalamin.
The growth constants for two normal, two spontaneously transformed, one chemically transformed, and one tumor cell line grown
in medium in which methionine was replaced by homocysteine were found to be proportional to the level of methionine synthetase.
The results demonstrate the utility of growth quantitation to study the methionine dependency of transformed cells.
Presented in part at the Conference on Differentiation and Carcinogenesis in Liver Cell Cultures sponsored by the New York
Academy of Sciences, October 11, 1979 (see reference 1). 相似文献
9.
Metabolism of Glycine in Primary Astroglial Cells: Synthesis of Creatine, Serine, and Glutathione 总被引:5,自引:1,他引:4
Ralf Dringen Stephan Verleysdonk Bernd Hamprecht Wieland Willker Dieter Leibfritz Annette Brand 《Journal of neurochemistry》1998,70(2):835-840
Abstract: The metabolism of [2-13 C]glycine in astrogliarich primary cultures obtained from brains of neonatal Wistar rats was investigated using 13 C NMR spectroscopy. After a 24-h incubation of the cells in a medium containing glucose, glutamate, cysteine, and [2-13 C]glycine, cell extracts and incubation media were analyzed for 13 C-labeled compounds. Labeled creatine, serine, and glutathione were identified in the cell extracts. If arginine and methionine were present during the incubation with [2-13 C]glycine, the amount of de novo synthesized [2-13 C]creatine was two-fold increased, and in addition, 13 C-labeled guanidinoacetate was found in cell extracts and in the media after 24 h of incubation. A major part of the [2-13 C]glycine was utilized for the synthesis of glutathione in astroglial cells. 13 C-labeled glutathione was found in the cell extracts as well as in the incubation medium. The presence of newly synthesized [2-13 C]serine, [3-13 C]serine, and [2,3-13 C]serine in the cell extracts and the incubation medium proves the capability of astroglial cells to synthesize serine out of glycine and to release serine. Therefore, astroglial cells are able to utilize glycine as a precursor for the synthesis of creatine and serine. This proves that at least one cell type of the brain is able to synthesize creatine. In addition, guanidinoacetate, the intermediate of creatine synthesis, is released by astrocytes and may be used for creatine synthesis by other cells, i.e., neurons. 相似文献
10.
Chlorophyll-protein levels and degree of thylakoid stacking in radish chloroplasts from high-light, low-light and bentazon-treated plants 总被引:3,自引:0,他引:3
Hartmut K. Lichtenthaler Gertrud Kuhn Ursula Prenzel Dieter Meier 《Physiologia plantarum》1982,56(2):183-188
Lemna gibba plants were incubated aseptically on medium containing labelled 10-7 M indole-3-acetic acid (IAA-1-14 C). Most of the radioactivity disappeared from the culture medium during a 24 h light period. A high percentage of the loss was due to photolysis and only a low percentage of the radioactivity was recovered in the plants. Uptake of 14 C by the plants was strongly stimulated by light. The radioactivity taken up by the plants was the sum of photosynthetically taken up 14 CO2 and 14 C taken up in IAA. Analyses with the indolo-α-pyrone fluorescence method revealed that the free IAA content was almost the same in plants grown in control and in IAA media for 5 h, whereas the amount of IAA which could be liberated by alkaline hydrolysis was doubled by the presence of IAA in the medium. 相似文献
11.
Allocation of carbon to growth, storage and respiration in the vegetative barley plant 总被引:12,自引:1,他引:11
J. F. FARRAR 《Plant, cell & environment》1980,3(2):97-105
Abstract. It is proposed that the growing plant can be divided into three compartments with reference to carbon: soluble, storage and structural. Experiments carried out at 10, 15, 20 and 30°C in the light followed changes in size of these compartments in barley plants 10–24 days old. The redistribution of I4 C photo-assimilated by 10 day old plants was monitored simultaneously. The soluble and storage compartments are a higher percentage of plant weight at lower temperatures, and are turned over rapidly at all temperatures; they form the source of respired 14 C. About 30% of the 14 C fixed enters structural material; in the first 24 h after labelling, for each unit of 14 C entering the structural compartment, between 0–9 (at 15°C) and 3.2 (at 30°C) units of 14 C are lost by respiration. At 15°C in the dark, respiratory loss of 14 C is initially from soluble and storage compartments; thereafter respiration of I4 C occurs at the expense of structural material. 相似文献
12.
A. M. Galle-Le Bastard C. Demandre A. Oursel M. Joseph P. Mazliak J. C. Kader 《Physiologia plantarum》2000,108(2):118-124
Boraginaceae seeds are particularly rich in Γ -linolenic acid (6,9,12-octadecatrienoic acid, Γ -18:3). In microsomes, the analysis of phosphatidylcholine (PC) molecular species by HPLC led to identification of 15 different molecular species; among them 4 contained Γ -18:3, mostly at position 2 of sn -glycerol. Time courses of acylation and desaturation in PC molecular species were examined when [14 C]oleoyl-CoA or [14 C]linoleoyl-CoA was provided as substrates to isolated microsomes. With [14 C]oleoyl-CoA or [14 C]linoleoyl-CoA and in the absence of NADH, 3 main labelled PC molecular species were found: 18:2/[14 C]18:1, 16:0/[14 C]18:1 and 18:1/[14 C]18:1. When NADH was present in the incubation medium, the fatty acids were progressively desaturated by the Δ12- and Δ6-desaturases successively (with [14 C]oleoyl-CoA as precursor) or by the Δ6-desaturase alone (with [14 C]linoleoyl-CoA as precursor). In both types of experiments, 7 final desaturation products in microsomes were evidenced; among them, 3 contained radioactive Γ -18:3, i.e . 18:2/[14 C] Γ -18:3, 18:1/[14 C] Γ -18:3 and 16:0/[14 C] Γ -18:3. While the Δ12-desaturase had no specificity for position on the glycerol backbone, labelled Γ -linolenic acid was recovered exclusively in the sn -2 position. 相似文献
13.
David A. Morris 《Physiologia plantarum》1981,52(2):251-256
When N 6 [8–14 C] furfuryladenine was applied to the intact root system of Pisum sativum L. cv. Meteor seedlings it was almost completely metabolised to other compounds within 24 h. Of the total activity recovered from the plants 94.5% was retained in the root system itself. 14 C was recovered in a number of ethanol-soluble compounds and in ribonucleic acid, deoxyribonucleic acid and protein fractions of roots, stems, leaves and axillary buds. In rapidly growing axillary buds released from apical dominance by removal of the shoot apex the combined nucleic acid fractions accounted for 63.3% of the total 14 C recovered from these organs. Xylem exudate collected from decapitated plants 0 to 12 h after supplying N 5 [8–14 C]furfuryladenine to the roots consistently contained a single major 14 C-labelled compound which, in three different solvent systems, had the same Rf values as a major endogenous cytokinin isolated from the xylem of unlabelled plants. The content of N 6 [8–14 C] furfuryladenine itself in the xylem exudate was always low and in some experiments it could not be detected.
It is suggested that part of the label from N6 [8- 14 CJfurfuryladenine taken up by the intact root system may have become incorporated in an endogenous cylokinin before export to the shoot. 相似文献
It is suggested that part of the label from N
14.
Abstract: The Ca2+ -dependent conformational alteration of the brain-specific S-100 protein was studied by reacting the protein with N -ethyl[2,3-14 C]maleimide in the absence and presence of Ca2+ and under denaturing conditions. Peptic hydrolysates of the 14 C-labeled protein were analyzed and fractionated by high-performance liquid chromatography. Labeled peptide fractions were characterized by high-voltage electrophoresis and TLC. A clear distinction could be made between two classes of sulfhydryl-containing fragments: (a) neutral, hydrophobic, and (b) acidic. Ca2+ markedly favored 14 C incorporation into the former components, whereas the latter were readily available only under denaturing conditions. 相似文献
15.
Succinic semialdehyde dehydrogenase (SSADH) catalyzes the NADP-dependent oxidation of succinic semialdehyde to succinate, the final step of the GABA shunt pathway. SSADH deficiency in humans is associated with excessive elevation of GABA and γ-hydroxybutyrate (GHB). Recent studies of SSADH-null mice show that elevated GABA and GHB are accompanied by reduced glutamine, a known precursor of the neurotransmitters glutamate and GABA. In this study, cerebral metabolism was investigated in urethane-anesthetized SSADH-null and wild-type 17-day-old mice by intraperitoneal infusion of [1,6-13 C2 ]glucose or [2-13 C]acetate for different periods. Cortical extracts were prepared and measured using high-resolution 1 H-[13 C] NMR spectroscopy. Compared with wild-type, levels of GABA, GHB, aspartate, and alanine were significantly higher in SSADH-null cortex, whereas glutamate, glutamine, and taurine were lower. 13 C Labeling from [1,6-13 C2 ]glucose, which is metabolized in neurons and glia, was significantly lower (expressed as μmol of 13 C incorporated per gram of brain tissue) for glutamate-(C4,C3), glutamine-C4, succinate-(C3/2), and aspartate-C3 in SSADH-null cortex, whereas Ala-C3 was higher and GABA-C2 unchanged. 13 C Labeling from [2-13 C]acetate, a glial substrate, was lower mainly in glutamine-C4 and glutamate-(C4,C3). GHB was labeled by both substrates in SSADH-null mice consistent with GABA as precursor. Our findings indicate that SSADH deficiency is associated with major alterations in glutamate and glutamine metabolism in glia and neurons with surprisingly lesser effects on GABA synthesis. 相似文献
16.
GAMMA-HYDROXYBUTYRATE DEGRADATION IN THE BRAIN IN VIVO: NEGLIGIBLE DIRECT CONVERSION TO GABA 总被引:3,自引:3,他引:0
Abstract— The metabolism of γ-hydroxybutyrate (GHB) was studied by following the fate of [1-14 C]GHB in mouse brain after an intravenous injection. Cerebral uptake of GHB was rapid and this substance disappeared from brain tissue with a half-life of approx 5 min. Degradation of [1-14 C]GHB took place in the brain since 14 C was incorporated in amino acids associated with the tricarboxylic acid cycle: the labelling pattern was consistent with the oxidation of GHB via succinate through the cycle, rather than with β-oxidation of GHB. Conversion of [14 C]GHB into [14 C]GABA prior to oxidation was negligible, thus it is unlikely that the pharmacological action of GHB would be mediated through GABA formation. [14 C]GHB oxidation also elicited the signs of metabolic compartmentation of the tricarboxylic acid cycle in the brain (glutamine/glutamate specific radioactivity ratio was about 4). 相似文献
17.
Effects of water stress and nocturnal temperature on carbon allocation in the perennial grass, Leymus chinensis 总被引:3,自引:0,他引:3
Water deficit and high temperature often occur simultaneously, but their effects on plants are usually investigated separately. The aim of this study was to test how interactions between water stress and nocturnal warming affect carbon allocation in the perennial grass, Leymus chinensis . Plant biomass, dry mass allocation, 14 C partitioning and carbon isotope composition (δ13 C) were measured. Severe and extreme water stress during nocturnal warming decreased the allocation of dry mass and 14 C partitioning below ground to the roots, but moderate water stress significantly increased the below-ground allocation of dry mass and 14 C, especially at the lower night temperature. The δ13 C values were more positive at day/night temperatures of 30/20°C than at 30/25°C, and greater in the roots than in the leaves. By plotting the δ13 C values of the leaves against the δ13 C values of the roots, the slopes of regressions were steeper at low than at high night temperature, also indicating that nocturnal warming reduces carbon allocation below ground to the roots. The results suggest that nocturnal warming may weaken acclimation during water stress in this species by regulating carbon allocation between source and sink organs. 相似文献
18.
This report demonstrates that during the torpor phase of hibernation, hamsters utilize 14 C and 13 C glucose in torpor-specific brain metabolic pathways. Microdialysis of 14 C glucose into the striatum rapidly induced a steady state labeling of extracellular fluid (ECF) lactate and labeling of tissue GABA, glutamate, glutamine, and alanine in ipsilateral and contralateral striata. The same tissue metabolites were labeled in cortex, hypothalamus, and brainstem after microdialysis of 14 C lactate into the lateral ventricle. Serine, aspartate, glycine, taurine, tyrosine, and methionine were not synthesized from glucose or lactate during torpor. ECF levels of amino and organic acids were low and unchanging during torpor and increased late during arousal to cenothermia. Labeled intracellular 14 C GABA and glutamate were not communicated to the striatal ECF or ventricular space during torpor. 13 C NMR demonstrated rapid formation of lactate and functional tricarboxylic acid cycles in GABAergic and glutamatergic neurons, and enrichment of glutamine and alanine after i.v. 13 C glucose. Large changes in tissue levels of amino acids occur prior to or during entrance into torpor but not during torpor. It is proposed that cerebral intracellular dehydration, the enlargement of ECF and the biochemistries associated with brain water homeostasis may have a role in regulating hibernation. 相似文献
19.
Air pollution in the past recorded in width and stable carbon isotope composition of annual growth rings of Douglas-fir 总被引:2,自引:2,他引:2
Abstract. Tree-ring indices (TRIs) of annual growth rings in stems of Douglas-fir ( Pseudotsuga menziesii ) growing near a copper smelter showed reduced growth during two multi-year time periods in the past. These periods coincided with World Wars I and II, which are known to represent periods of particularly high SO2 emissions from the smelter. Reduced growth was correlated with less negative stable carbon isotope composition (δ13 C) in cellulose purified from wood formed in such years. Based on current models for 13 C/12 C in plants, these results indicate that exposure to air pollution resulted in reduced concentration of CO2 in the intercellular air spaces of the needles. This is consistent with the hypothesis that stomatal closure resulted in impaired photosynthesis and reduced growth during past episodes of high air pollution. The pollution-related change in δ13 C was superimposed on a change with time in δ13 C, independent of growth, by - 1.4 per mil from 1902 to 1984. 相似文献
20.
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-14 C] l -methionine ([14 C]SAM) generated by adenosyl transfer from ATP to [methyl-14 C] l -methionine is quantitated by use of a SAM-consuming transmethylation reaction. Catechol O -methyltransferase (COMT), prepared from rat liver, transfers the methyl-14 C group of SAM to 3,4-dihydroxybenzoic acid. The 14 C-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. 相似文献