Simultaneous analysis of homocysteine and methionine in plasma

The new isocratic cation exchange method separates up to eight different amino thiols. The separated sample components are detected electrochemically using a gold electrode and the integrated pulsed amperometry. The eluent composition is, for example, 0.15 M sodium perchlorate, 0.02 M perchloric acid and 5% acetonitrile. The report describes the optimization of chromatographic parameters such as column diameter and eluent composition. Quantitative performance is discussed for eight different amino thiols using standards. Also presented is a long term quantitative study for homocysteine and methionine in plasma samples. The preparation of plasma samples is simpler than with the previously reported version of the method. Only a reduction step is required, and neither column switching nor derivatization are necessary.     

非天然氨基酸N-保护的D-(L-)4-吡啶丙氨酸的合成研究

合成了非天然氨基酸N 保护的D (L ) 4 吡啶丙氨酸 ,其结构分别通过旋光度、核磁共振、红外、元素分析得到确证。     

The metabolism of D- and L-3-hydroxybutyrate in developing rat brain

The incorporation of L- and D-3-hydroxybutyrate into rat brain protein, lipid, and amino acids during development was studied. L-3-Hydroxybutyrate was found to label brain protein and amino acids in addition to sterols and fatty acids throughout the first 32 postnatal days. Age related changes in L- and D-3-hydroxybutyrate labeling of protein and amino acids were similar. Whereas L-3-hydroxybutyrate incorporation into brain lipids rose sharply between 6-15 days of age, D-3-HOB incorporation into the lipid fraction gradually increased from birth through the age of 15 days. Incorporation by both isomers into lipid was greatest during the third week of suckling and then declined when the animals were weaned. At 15 days of age, the distribution of L-3-hydroxybutyrate into glutamate, glutamine + aspartate, and gamma-aminobutyrate was similar to that obtained with D-3-hydroxybutyrate. L-3-Hydroxybutyrate was poorly oxidized to CO2 by brain slices and mitochondria. Oxidation capacity was maximal from 15-21 days of age for both isomers. The activity of L-3-hydroxybutyrl-CoA ligase increased between 6-28 days of age, and its increase is well correlated with the developmental pattern of L-3-hydroxybutyrate incorporation and mitochondrial oxidation. L-3-Hydroxybutyrate was not detected in the blood of palmitate-injected pups or fasted adult animals. These results suggest that although L-3-hydroxybutyrate can be utilized for the synthesis of brain components during development, its negligible blood concentration precludes a significant contribution to either tissue synthesis or energy balance during the suckling period.     

Human methionine aminopeptidase type 2 in complex with L- and D-methionine

Human methionine aminopeptidase type 2 (hMetAP-2) was identified as the molecular target of anti-angiogenic agents such as fumagillin and its analogues. We describe here the crystal structure of hMetAP-2 in complex with l-methionine and d-methionine at 1.9 and 2.0A resolution, respectively. The comparison of the structure of the two complexes establishes the basis of enantiomer discrimination and provides some considerations for the design of selective MetAP-2 inhibitors.     

树脂载体固定S-腺苷甲硫氨酸合成酶的研究

目的:筛选一种适合S-腺苷甲硫氨酸合成酶固定化的树脂载体,进行固定化工艺优化及固定化酶性质研究。方法:以固定化率和表观酶活回收率为指标,筛选固定化效果最佳的一种树脂,采用单因素实验对固定化条件进行优化。结果:阴离子交换树脂载体ESR-2表现出最优的固定化率(94.03%)和酶活回收率(47.45%);最佳固定化条件为加酶量4U/g、pH 8.0、15℃吸附10h,最佳条件下固定化酶表观酶活为2.1U/g,表观酶活回收率达51.6%。固定化酶的最适pH为8.5,最适温度为35℃,连续反应10批次后酶活剩余77.92%。结论:树脂载体ESR-2固定化S-腺苷甲硫氨酸合成酶酶活及稳定性较好,能够用于S-腺苷甲硫氨酸的工业化大规模生产。     

Simultaneous determination of methionine sulfoxide and methionine in blood plasma using gas chromatography-mass spectrometry

Methionine sulfoxide is an oxidation product of methionine with reactive oxygen species via 2-electron-dependent mechanism. Such oxidants can be generated from activated neutrophils; therefore, methionine sulfoxide can be regarded as a biomarker of oxidative stress in vivo. We describe here a method for the simultaneous determination of methionine sulfoxide and methionine in blood plasma using gas chromatography-mass spectrometry with isotopically labeled compounds as internal standards. This method comprises the inclusion of [Me-13C, Me-2H(3)]methionine sulfoxide and [Me-13C, Me-2H(3)]methionine into plasma, the removal of plasma proteins using acetonitrile, the purification of amino acids with cation-exchange chromatography, and the derivatization of methionine sulfoxide and methionine to their corresponding tert-butyldimethylsilyl derivatives using N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide. Quantitation was performed by electron impact mode. The levels of methionine sulfoxide in healthy human blood plasma were 4.0 +/- 1.0 microM (means +/- SD, n = 8), indicating that approximately 10% of methionine is detected as the oxidized form in healthy human plasma. The ratio of methionine sulfoxide in total methionine increased with treatment of human blood with phorbol 12-myristate 13-acetate, while this ratio remained constant in plasma from alloxan-induced hyperglycemic rabbits. These results indicate that this method is applicable for plasma samples and methionine sulfoxide can represent oxidative stress caused by nonradical oxidation in vivo.     

Determination of D- and L-enantiomers of methionine and [2H3]methionine in plasma by gas chromatography-mass spectrometry

A method for the stereoselective determination of D- and L-enantiomers of both methionine and [(2)H3]methionine in rat plasma was developed using gas chromatography-mass spectrometry with selected-ion monitoring (GC-MS-SIM). DL-[(2)H7]Methionine was used as analytical internal standard to account for losses associated with the extraction, derivatization and chromatography. The amino acids were purified by cation-exchange chromatography using BondElut SCX cartridge and derivatized with HCl in methanol to form methyl ester followed by subsequent N-acylation with optically active (+)-alpha-methoxy-alpha-trifluoromethylphenylacetyl chloride to form diastereomeric amide. Quantification was performed by SIM of the molecular-related ions of the diastereomers on the chemical ionization mode. Endogenous L-methionine concentrations in 50 microl of rat plasma were measured with relative intra- and inter-day precision of 4.0 and 6.3%, respectively. The intra- and inter-day reproducibility in the amounts of D- and L-[(2)H3]methionine determined were in good agreement with actual amount added.     

离子交换法分离D-天冬氨酸和L-丙氨酸

对离子交换法分离D-天冬氨酸和L-丙氨酸的工艺条件进行了研究。综合考虑树脂对D-天冬氨酸和L-丙氨酸的吸附容量及相对选择系数,选择了一种适合该体系分离的树脂—XH-1,并对吸附条件及洗脱条件进行了研究,确定了最佳工艺条件,为今后工业应用提供一定的依据。     

L－亮氨酸Schiff碱Cu（Ⅱ）、Ni（Ⅱ）配合物的合成及抑菌活性

合成了Ｌ－亮氨酸Ｓｃｈｉｆｆ碱的Ｃｕ（Ⅱ）、Ｎｉ（Ⅱ）配合物,其化学结构由红外光谱、元素分析、热重分析及摩尔电导等证实。对配合物进行了抑菌测试。     

L－亮氨酸Schiff碱Cu（Ⅱ）、Ni（Ⅱ）配合物的合成及抑菌活性

合成了Ｌ－亮氨酸Ｓｃｈｉｆｆ碱的Ｃｕ（Ⅱ）、Ｎｉ（Ⅱ）配合物,其化学结构由红外光谱、元素分析、热重分析及摩尔电导等证实。对配合物进行了抑菌测试。     

Asymmetrical radical formation in D- and L-alanines irradiated with yttrium-90 beta-rays.

Radical formation in 90Y-beta-irradiated D- and L-alanines was studied using ESR. It was observed that the relative radical concentration by beta-irradiation was distinguishably (13.9-21.5%) more in D-alanine than in L-alanine. Discussion was made on the possible mechanisms for the observed results.     

Evolution of methionine initiator and phenylalanine transfer RNAs

Summary Sequence data from methionine initiator and phenylalanine transfer RNAs were used to construct phylogenetic trees by the maximum parsimony method. Although eukaryotes, prokaryotes and chloroplasts appear related to a common ancestor, no firm conclusion can be drawn at this time about mitochondrial-coded transfer RNAs. tRNA evolution is not appropriately described by random hit models, since the various regions of the molecule differ sharply in their mutational fixation rates. Hot mutational spots are identified in the TC, the amino acceptor and the upper anticodon stems; the D arm and the loop areas on the other hand are highly conserved. Crucial tertiary interactions are thus essentially preserved while most of the double helical domain undergoes base pair interchange. Transitions are about half as costly as transversions, suggesting that base pair interchanges proceed mostly through G-U and A -C intermediates. There is a preponderance of replacements starting from G and C but this bias appears to follow the high G + C content of the easily mutated base paired regions.