血清Hcy、FA、VitB12水平及H.pylori感染与脑梗死的相关性研究

目的：探讨脑梗死（cerebral infarction,CI）患者血清同型半胱氨酸（homocysteine,Hcy）、叶酸（folate,FA）、维生素B12（Vitamin B12,VitBl2）水平及幽门螺杆菌（H_pylori）感染与脑梗死的关系,为预防和治疗脑梗死提供参考依据。方法：选择本科收治的132例脑梗死患者和同期81例健康对照者为研究对象,检测和比较其血清同型半胱氨酸（Hey）、叶酸（FA）、VitB12水平及HP-IgG抗体。结果：（1）脑梗死患者H．pylori的感染率为50．76％,显著高于健康对照组（35．80％）（X2=0．54,P〈0．05）;（2）脑梗死患者血清Hey[（20．02±8．84）μmol／L]和FA水平[（14．47±6．38）ng／mL）]与健康对照组[（12．36±4．97）μmol／L,（16．82±11．43）ng／mL）]比较,均具有显著差异（P〈0．01,P〈0．01）;而VitB12水平与健康对照组比较无统计学意义（P〉0．05）;（3）脑梗死患者中,HP-IgG阳性的患者Hey水平[（24．20±8．81）μmol／L]明显高于HP-IgG阴性的患者[（15．71±6．53）μmol／L]（P〈0．01）,血清FA水平[（14．59±7．54）ng／mL）]明显低于于HP-IgG阴性的患者[（14．43±4．98）ng／mL]（P〈0．05）,而两组之间VitBl2水平比较无明显差异（P〉0．05）;HP—IgG阳性的脑梗死患者Hey水平[（24．20±8．81）bLmol／L]与HP—IgG阳性的健康对照组[（13．25±5．24）μmol／L]相比,差异显著（P〈0．05）,FA,VitB12水平低于健康对照组,但并无显著差异（P〉0．05）.结论：脑梗死患者H．pylori的感染率高于健康人群;H．pylori感染可能影响脑梗死患者Hey的代谢,导致Hey水平升高,促进了脑梗死的发生和发展。     

Brain Protein Synthesis in the Conscious Rat Using L-[35S]Methionine: Relationship of Methionine Specific Activity Between Plasma and Precursor Compartment and Evaluation of Methionine Metabolic Pathways

The method previously developed for the measurement of rates of methionine incorporation into brain proteins assumed that methionine derived from protein degradation did not recycle into the precursor pool for protein synthesis and that the metabolism of methionine via the transmethylation pathway was negligible. To evaluate the degree of recycling, we have compared, under steady-state conditions, the specific activity of L-[35S] methionine in the tRNA-bound pool to that of plasma. The relative contribution of methionine from protein degradation to the precursor pool was 26%. Under the same conditions, the relative rate of methionine flux into the transmethylation cycle was estimated to be 10% of the rate of methionine incorporation into brain proteins. These results indicate the following: (a) there is significant recycling of unlabeled methionine derived from protein degradation in brain; and (b) the metabolism of methionine is directed mainly towards protein synthesis. At normal plasma amino acid levels, methionine is the amino acid which, to date, presents the lowest degree of dilution in the precursor pool for protein synthesis. L-[35S]-Methionine, therefore, presents radiobiochemical properties required to measure, with minimal underestimation, rates of brain protein synthesis in vivo.     

同型半胱氨酸与不同类型卒中的相关性研究

目的：探讨同型半胱氨酸（Hcy）与不同类型脑卒中的关系,并对高Hcy血症成因作初步分析。方法：测定225例缺血性脑卒中和40例出血性脑卒中患者以及85例同龄健康受试者的血浆Hcy水平以及叶酸、维生素B12的浓度,将缺血性卒中按照TOAST分型分为不同临床亚组--动脉粥样硬化性脑血栓形成组,腔隙性脑梗死组,心源性脑栓塞组以及其他或不明原因脑梗死组,并分别与健康组进行对照研究。结果：血浆同型半胱氨酸平均水平在动脉粥样硬化性脑梗死组患者为（16.19±4.35）μmol/L,腔隙性脑梗死患者为（16.89±6.41）μmol/L,心源性脑栓塞组为（18.23±4.83）μmol/L,其他或不明原因脑梗死患者为（17.31±2.56）μmol/L,脑出血组患者为（14.91±4.54）μmol/L,均高于对照组（7.20±7.91）μmol/L,P〈0.05;各缺血性卒中组间同型半胱氨酸水平差异无显著性（P〈0.05）;缺血性卒中组患者血浆同型半胱氨酸水平高于出血性卒中组（P〈0.05）。卒中各组叶酸和维生素B12浓度均显著低于对照组（P〈0.05）。结论：血浆同型半胱氨酸在不同类型卒中中均升高,高血浆Hcy水平可能是脑卒中的独立危险因素,叶酸和VitB12缺乏可能是导致高Hcy血症的重要原因。     

A mathematical model of the methionine cycle

Building on the work of Martinov et al. (2000), a mathematical model is developed for the methionine cycle. A large amount of information is available about the enzymes that catalyse individual reaction steps in the cycle, from methionine to S-adenosylmethionine to S-adenosylhomocysteine to homocysteine, and the removal of mass from the cycle by the conversion of homocysteine to cystathionine. Nevertheless, the behavior of the cycle is very complicated since many substrates alter the activities of the enzymes in the reactions that produce them, and some can also alter the activities of other enzymes in the cycle. The model consists of four differential equations, based on known reaction kinetics, that can be solved to give the time course of the concentrations of the four main substrates in the cycle under various circumstances. We show that the behavior of the model in response to genetic abnormalities and dietary deficiencies is similar to the changes seen in a wide variety of experimental studies. We conduct computational "experiments" that give understanding of the regulatory behavior of the methionine cycle under normal conditions and the behavior in the presence of genetic variation and dietary deficiencies.     

Biosynthesis of Polyamines in Mouse Brain: Effects of Methionine Sulfoximine and Adenosylhomocysteine

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, [1,4-¹⁴C]putrescine, the specific radioactivity (sra) of the newly formed [¹⁴C]spermidine remained unchanged. Conversely, after i.vt. l -[3,4-¹⁴C]methionine, the other polyamine precursor, significantly higher sra values for [¹⁴C]spermidine and [¹⁴C]spermine were recorded in the brains of the MSO-treated animals. [¹⁴C] S - adenosylmethionine in the brain of the MSO-treated animals was also more highly labeled following [1-¹⁴C]-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 [3,4-¹⁴C]-methionine. The results of these experiments show both significantly lower sra values for [¹⁴C]spermidine and [¹⁴C]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.     

血清Hcy，叶酸和维生素B12在胃癌及其癌前疾病中的作用

目的:探讨血清同型半胱氨酸(Hcy)、叶酸以及维生素B12在胃癌及癌前疾病中的水平及临床意义。方法:收集2014年1月至2016年8月我院收治的100例胃癌患者(胃癌组),及100例胃良性病变患者包括41例胃炎、34例胃溃疡、25例胃息肉(癌前病变组),并于同期随机选择200例健康体检者为对照组,采用循环酶法测定三组的血清Hcy,电化学发光免疫分析法测定叶酸及维生素B12水平,并分析各指标与胃癌临床病理特征的关系。结果:胃癌组、癌前病变组血清Hcy水平均高于对照组,叶酸及维生素B12水平均低于对照组,并且胃癌组血清Hcy水平高于癌前病变组,叶酸及维生素B12水平低于癌前病变组,差异有统计学意义(P0.05)。Ⅲ+Ⅳ期胃癌患者Hcy水平高于Ⅰ+Ⅱ期,进展期患者Hcy水平高于早期,有淋巴结转移患者Hcy水平高于无转移者,差异有统计学意义(P0.05);Hcy表达与性别、年龄、病变位置以及分化程度无关,差异无统计学意义(P0.05)。叶酸、维生素B12的表达在胃癌患者中与各临床病理特征(性别、年龄、TNM分期、肿瘤浸润深度、病变位置、有无淋巴结转移、分化程度)无明显关系,差异无统计学意义(P0.05)。结论:血清Hcy在胃癌患者中呈高水平表达,而叶酸及维生素B12呈低水平表达,联合检测三种指标有助于早期区分胃癌及癌前病变,同时血清Hcy还可能参与了胃癌的发生发展过程。Hcy、叶酸及维生素B12可作为早期鉴别诊断胃癌及其癌前病变的重要指标。     

Lipid Composition of the Brain in the Vitamin B12-Deficient Fruit Bat (Rousettus aegyptiacus) with Neurological Impairment

Abstract: The Egyptian fruit bat Rousettus aegyptiacus develops severe vitamin B₁₂ deficiency when fed a diet of fresh peeled fruit and water. In a group of bats fed this diet, B₁₂ concentrations in the serum and brain were low, and neurological impairment, evidenced by deficient or absent hindlimb groping or grasping ability and climbing difficulties, was manifest. Control bats fed the identical diet supplemented with B₁₂ showed no such changes. Fatty acid analysis of whole brain homogenates showed a higher level of 20:4 in the deficient group. Phosphatidylcholine showed a marginally higher percentage of 18:3. The total percentage of branched chain fatty acids of phos-phatidylethanolamine was four times higher in deficient brains, comprising 2% of the total. Sphingomyelin showed a slightly higher percentage of 15:0, and a significantly lower percentage of long chain fatty acids C-24 and longer ( p < 0.01). The compositions of nonhydroxy fatty acids in cerebroside were unchanged. Examination of phospholipids showed that 8.9 ± 0.4% of total phosphorus was present as sphingomyelin in deficient bats, compared with 11.9 ± 1.2% in control animals (p < 0.05). There were no statistically significant differences in the concentrations of total brain lipid, protein, phospholipid, glycosphingolipid, cholesterol and plasmalogen between B₁₂-deficient and control bats.     

Development and Regional Distribution of Methionine Synthetase in Rabbit Brain

The development and regional distribution of methionine synthetase (EC 2.1.1.13) in rabbit brain was determined. In adult rabbits, the specific activity (units per milligram protein) of methionine synthetase in cortex, cerebellum, brain stem, and corpus striatum was comparable to the specific activity in whole brain (0.5 units/mg). In the first few weeks of life, the specific activity of methionine synthetase in whole rabbit brain declined from a value of 1.1 units/mg at 1 day of age to 0.5 units/mg at 6–10 weeks. Two-year-old rabbits had 0.6 units/mg in whole brain. These results show that: (a) methionine synthetase is distributed widely in mammalian brain and (b) methionine synthetase activity in brain declines relatively little with development.     

Source of Methyl Groups in Brain and Nerve Tissue in the Rat

Previous studies that demonstrated that mouse brain accumulated significantly more radioactivity from subcutaneously administered 5-methyltetrahydrofolate labelled in the methyl group compared to the label in the folate moiety are open to two interpretations. The methyl group could have been transferred to another compound (probably methionine) prior to its transport into the brain. Alternatively, if plasma 5-methyltetrahydrofolate per se is significantly involved in the provision of methyl groups to brain and nerve tissue it would be expected that the folate moiety would be returned to the plasma to complete the cycle and thus would appear not to have been taken up. In this article, using competition experiments that exploit the differences in the mechanism of transport of methionine and 5-methyltetrahydrofolate into brain and nerve, evidence is presented that in the rat the methyl group of 5-methyltetrahydrofolate is transported after its conversion to methionine.     

Biosynthesis of vitamin B-12 Part I. Role of the ribosomal proteins in vitamin B-12 biosynthesis

1. 70 S ribosomes isolated from strains of Escherichia coli 113-3, K₁₂ and B take part in vitamin B-12 biosynthesis from AdoCbi-GDP, NAD and dimethylbenzimidazole in the presence of enzymes of the cytosol fraction. 2. 70 S ribosomes from E. coli 113-3 bind Ado[⁵⁸Co]Cbi-GDP. This reaction is independent of fusidic acid. 3. Proteins from 5 S RNA complex as well as L2 protein isolated from E. coli 113-3 ribosomes catalyze vitamin B-12 biosynthesis. The main catalytic function in this reaction is performed by protein L18.4. Vitamin B-12 biosynthesis proceeding in the presence of isolated ribosomal proteins is inhibited by fusidic acid, chloramphenicol and vernamycin but not by erythromycin. 5. Vitamin B-12 synthesized in the presence of isolated ribosomal proteins is biologically active.     

Incorporation of Intracisternally Administered l-[methyl-3H]Methionine and S-Adenosyl-l-[methyl-3H]-Methionine into Rat Brain Phospholipids

The incorporation of intracisternally injected L-[methyl-3H]methionine [( 3H]Met) or S-adenosyl-L-[methyl-3H]methionine (Ado[3H]Met) into rat brain AdoMet and phospholipid pools was examined. When [3H]Met was administered, both AdoMet and phospholipid pools were labeled. However, exogenously injected Ado[3H]Met did not serve as a substrate for phospholipid-N-methyltransferases. It was concluded that only Ado[3H]Met formed in situ was utilized to methylate phospholipids and that this process was initiated on the cytoplasmic side of the membrane. The apparent biological half-life in brainstem of phosphatidyl-N-monomethylethanolamine and phosphatidyl-N,N-dimethylethanolamine formed from [3H]Met was 1.4 and 1.7 days, respectively. The half-life of phosphatidylcholine could not be determined due to interference from peripheral sources.     

信号蛋白中甲硫氨酸残基的可逆性氧化和甲硫氨酸亚砜还原酶

含硫氨基酸甲硫氨酸在体内易被胞内、外活性氧氧化为甲硫氨酸-R,S-亚砜。蛋白质肽链中的甲硫氨酸残基被氧化后,蛋白活性发生显著改变,如钙调素与钙调素结合蛋白亲和力的下降、钙离子/钙调素依赖性蛋白激酶Ⅱ的激活、钾离子通道ShC/B失活动力学的改变。多数生物都存在一个msrA基因和1～3个msrB基因,编码两种序列和结构都明显不同的酶:甲硫氨酸亚砜还原酶A(MsrA)和甲硫氨酸亚砜还原酶B(MsrB),分别还原甲硫氨酸-S-亚砜和甲硫氨酸-R-亚砜。两种酶的催化机制基本相同,其活性中心结构互为镜像。两种还原酶分布于体内不同器官及各种亚细胞结构。对于MsrA活性的研究,已有30年的历史,最初主要集中在低等生物,已发现MsrA对于延缓衰老和神经退行性疾病具有重要作用,也是致病菌的主要毒力因子。最近10年对MsrB也进行了系统研究,并取得了重要进展。人们正在逐渐认识到这些酶在细胞信号蛋白分子活性调节中的重要作用。     

急性脑梗死患者血浆同型半胱氨酸水平及其相关因素分析*

目的:探讨急性脑梗死患者血浆同型半胱氨酸水平及相关因素。方法:采用高效液相色谱法检测232例急性脑梗死患者血浆Hcy水平,并对其相关因素进行统计学分析。结果:急性脑梗死组患者血浆Hcy水平明显升高(P<0.05);并与叶酸及维生素B12水平显著相关。不同年龄段急性脑梗死患者血浆Hcy水平具有差异。并与颈动脉粥样硬化斑块相关联。结论:血浆Hcy水平增高是脑梗死的危险因素之一,并与患者年龄、血液中叶酸、维生素B12水平及脑梗死性质相关联。     

维生素B12的光解研究及发酵液中维生素B12检测新方法的建立

采用HPLC检测法研究5,脱氧腺苷钴胺素和甲基基钴胺素的水溶液在不同光源及不同照度下的光解情况,结果表明随着光能量的增加光解速度加快。利用脱氧腺苷钴胺素的光解性质,探索了一种检测发酵液中维生素B12含量的新方法。将含有钴胺素的细胞破碎液完全光解后,测定光解后的产物羟基钴胺素,以此来确定维生素B12产量。此方法简便快速、重复性好,可应用于发酵生产维生素B12的各个环节。     

Methionine sulfoxide reductase: Chemistry,substrate binding,recycling process and oxidase activity

Three classes of methionine sulfoxide reductases are known: MsrA and MsrB which are implicated stereo-selectively in the repair of protein oxidized on their methionine residues; and fRMsr, discovered more recently, which binds and reduces selectively free L-Met-R-O. It is now well established that the chemical mechanism of the reductase step passes through formation of a sulfenic acid intermediate. The oxidized catalytic cysteine can then be recycled by either Trx when a recycling cysteine is operative or a reductant like glutathione in the absence of recycling cysteine which is the case for 30% of the MsrBs. Recently, it was shown that a subclass of MsrAs with two recycling cysteines displays an oxidase activity. This reverse activity needs the accumulation of the sulfenic acid intermediate. The present review focuses on recent insights into the catalytic mechanism of action of the Msrs based on kinetic studies, theoretical chemistry investigations and new structural data. Major attention is placed on how the sulfenic acid intermediate can be formed and the oxidized catalytic cysteine returns back to its reduced form.     

血清同型半胱氨酸、叶酸、维生素B12水平与冠状动脉病变严重程度的相关性分析

摘要 目的：探讨血清同型半胱氨酸(homocysteine, Hcy)、叶酸、维生素B12水平与冠状动脉病变严重程度的相关性。方法：选取经冠脉造影检查确诊的稳定期冠心病患者220例为研究组,并以同期健康查体志愿者100例为对照组。检测和比较两组血清Hcy、叶酸、维生素B12和N -末端脑钠肽前体(N-terminal brain natriuretic peptide precursor,NT-proBNP)水平。研究组根据冠脉造影情况进行SYNTAX评分评价,通过心脏超声检查检测左室射血分数(left ventricular ejection fraction,LVEF),确定冠脉病变严重程度。比较研究组SYNTAX低分组(1～22分)、中分组(23～32分)和高分组(≥33分)患者上述各指标水平,并分析研究组血清Hcy、叶酸、维生素B12水平与其血清NT-proBNP 水平、SYNTAX评分和LVEF的关系。结果：与对照组比较,研究组血清Hcy和NT-proBNP水平升高而血清叶酸、维生素B12水平降低(P＜0.05)。研究组SYNTAX评分和LVEF分别为(28.76±6.58)分和(47.33±8.66)%,SYNTAX中分和高分患者血清Hcy和NT-proBNP水平高于SYNTAX低分患者而血清叶酸、维生素B12水平和LVEF则低于SYNTAX低分患者,SYNTAX高分患者血清Hcy和NT-proBNP水平高于SYNTAX中分患者而血清叶酸、维生素B12水平和LVEF则低于SYNTAX中分患者(P＜0.05)。Pearson线性相关分析结果显示研究组血清Hcy水平与其血清NT-proBNP 水平、SYNTAX评分均呈正相关(r=0.881,0.793,P＜0.05),与其LVEF则呈负相关(r=-0.876,P＜0.05);而其血清叶酸、维生素B12水平与其血清NT-proBNP 水平、SYNTAX评分均呈负相关(叶酸：r=-0.786,-0.825;维生素B12：r=-0.884,-0.818,P＜0.05),与其LVEF则呈正相关(r=0.893,0.859,P＜0.05)。结论：血清Hcy是冠心病的重要危险因素,其水平随着冠状动脉病变程度加重而升高;血清叶酸、维生素B12是冠心病的保护因素,其水平随着冠状动脉病变程度加重而降低。     

Methionine Sulfoximine Prevents the Accumulation of Large Neutral Amino Acids in Brain of Portacaval-Shunted Rats

Portal-systemic shunting and hyperammonemia lead to an accumulation of the large neutral amino acids in brain and apparently alter transport of neutral amino acids across the blood-brain barrier. It has been proposed that portal-systemic shunting leads to a high brain concentration of glutamine, a product of cerebral ammonia detoxification, and thereby affects the transport of other neutral amino acids across the blood-brain barrier. To test this hypothesis, rats with a portacaval shunt were treated with L-methionine-dl-sulfoximine (MSO), an inhibitor of glutamine synthesis. Treatment with MSO resulted in lower concentrations of the neutral amino acids in brain of portacaval-shunted rats and a higher brain ammonia concentration, compared with untreated shunted rats. These results suggest that the accumulation of neutral amino acids in brain after portacaval shunt depends on the increased synthesis of glutamine in brain.     

Plasma total homocysteine and subarachnoid haemorrhage in a co-factor replete population

Summary. Mild hyperhomocysteinaemia is a postulated risk factor for occlusive vascular disease, including stroke. Subarachnoid haemorrhage (SAH) has an annual incidence of 10–20 per 100,000 and accounts for 5–10% of all strokes. Measurement of plasma total homocysteine (tHcy) in a cohort of vitamin B12 and folate replete patients did not reveal any association between tHcy and the aetiology of SAH. Received November 6, 2000 Accepted February 12, 2001     

The Role of Vitamin B12 Binding In the Uptake of the Vitamin By Euglena Gracilis

The uptake of [⁵⁷Co]B₁₃ (cyanocobalamin) by Euglena gracilis strain Z (ATCC 12716) occurred in 2 distinct phases-an initial rapid phase followed by a slower secondary phase. This secondary phase appeared after the saturation of the binding sites involved in the initial rapid phase and was energy-dependent and completely inhibited by 2,4-dinitrophenot, KCN and sodium azide. the subcellular localization of labeled cyanocobalamin taken up by the cell was mostly contained in the chloroplast fraction. the time course and the saturation kinetics of B₁₂ uptake by purified chloroplast fraction indicated that this fraction and the intact cell had a similar affinity for the vitamin B₁₂. This suggested that the chloroplasts contained the binding sites for vitamin ₁₂ and might regulate the uptake process in the intact cell. the kinetic properties of the overall ₁₂ uptake mechanism suggested that the initial phase represent the binding of vitamin ₁₂ to the available sites on the chloroplast. the secondary phase may represent the de novo synthesis of new binding sites.