甘氨酸在心血管疾病中的保护作用

甘氨酸是一种结构最简单的氨基酸,在动物体内广泛存在,为一碳、蛋白质、多肽、核苷酸类、卟啉类以及胆盐代谢中的关键物质.甘氨酸不仅是中枢神经系统的抑制性神经递质,而且还广泛参与代谢调控、抗氧化、抗凋亡等病理生理学过程.本文就甘氨酸在心肌缺血、高血压和高血糖等引起的心血管疾病中的作用进行综述.     

甘氨酸神经递质研究进展

甘氨酸是化学结构最简单的氨基酸,但具有复杂的功能。甘氨酸在中枢神经系统中是介导快速抑制性神经传递的一种重要的神经递质,在控制神经元兴奋性方面发挥重要作用。就其神经递质功能对甘氨酸的生物合成、释放与调控以及作用模式等方面的近年研究进展做一综述,对甘氨酸神经递质的全面认识将有益于炎性痛、痉挛状态以及癫痫等中枢神经系统疾病的诊断、预防及治疗。     

真核蛋白质中G-patch结构域的结构和功能研究

G-patch是广泛存在真核生物蛋白质中的保守结构域,含有六个高度保守的甘氨酸残基,推测它是一种RNA结合结构域,其功能与RNA代谢有关.     

NAD~+对小麦叶片线粒体甘氨酸氧化和三羧酸代谢的调节

外源NAD~+对小麦叶片线粒体内甘氨酸、苹果酸及α—酮戊二酸氧化都有促进作用。当几种呼吸底物同时存在时,其中甘氨酸的氧化抑制了其他底物的同时氧化,因为催化这两类废物氧化的酶对NAD~+的亲和力和对NADH/NAD~+比值的敏感程度有差异,催化甘氨酸氧化的甘氨酸脱羧酶对线粒体基质内可利用的NAD~+的亲和力分别比苹果酸脱氢酶和α—酮戊二酸脱氢酶的亲和力大约1或2倍。另外,甘氨酸亦可通过保持线粒体基质内高NADH/NAD~+比值来影响三羧酸环的正常代谢。     

定量分析丝氨酸/甘氨酸转换影响胃癌细胞增殖的动力学机制

目的 胃癌（GC）严重影响人类的健康生活,研究表明其与丝氨酸/甘氨酸代谢密切相关。丝氨酸/甘氨酸代谢对于肿瘤细胞的增殖能力具有重要影响。本文的研究目的是探究丝氨酸/甘氨酸代谢能够影响胃癌细胞增殖能力的分子机制。方法 本文通过一种基于随机和非梯度系统的势能景观所建立的大型代谢网络动力学建模方法,构建了一个稳定的胃癌细胞代谢动力学模型。基于对模型的调控,定量分析丝氨酸/甘氨酸代谢影响胃癌细胞增殖的动力学机制。对一般代谢网络动力学方程添加随机噪声,通过随机动力学分解得到代谢网络参数空间的李雅普诺夫（Lyapunov）函数。进一步减少与随机波动相关的Lyapunov函数变化,从而得到稳定的代谢网络。结果 在动力学参数不足的情况下,成功构建了胃癌细胞代谢网络的动力学模型。当胞外丝氨酸可用时,模型优先消耗丝氨酸;当甘氨酸生成丝氨酸的速率增加时,模型显著上调生成S-腺苷甲硫氨酸（SAM）和S-腺苷同型半胱氨酸（SAH）的稳态通量。结论 本文证明了胃癌细胞对于丝氨酸的优先摄取以及丝氨酸/甘氨酸转化速率对SAM生成的重要作用,其可能通过调节细胞甲基化进程影响胃癌细胞的增殖能力,为靶向丝氨酸/甘氨酸代谢的癌症治疗提供了新的思路和方向。     

小鼠脑内甘氨酸含量在缺氧预适应中的变化

在小鼠重复缺氧预适应过程中,用HPLC方法,测定其全脑与不同脑区中的甘氨酸含量。结果表明,随着动物对低氧耐受性的增高,其全脑、间脑,特别是海马、脑干中的甘氨酸含量升高。结果提示,甘氨酸作为抑制性递质对低氧预适应的形成具有正面影响。     

L-异亮氨酸和甘氨酸对大肠杆菌表达与分泌邻苯二酚2,3-双加氧酶的作用

证实了甘氨酸与L-异亮氨酸对大肠杆菌表达邻苯二酚2,3-双加氧酶(CatO_2ase)的促进作用和甘氨酸促使该酶分泌至胞外培养基中的作用.产酶量高低和分泌量多少与培养基种类、甘氨酸和L-异亮氨酸的浓度以及培养时间等因素有关.在甘氨酸存在的情况下,胞壁对溶菌酶的敏感性有所增加,超微形态似有变化,还存在其他物质的伴随分泌,故甘氨酸可能是引起细胞壁结构的改变而导致邻苯二酚2,3-双加氧酶等胞内容物被动分泌至胞外.     

L-异亮氨酸和甘氨酸对大肠杆菌表达与分泌邻苯二酚2,3-双加氧酶的作用

证实了甘氨酸与L-异亮氨酸对大肠杆菌表达邻苯二酚2,3-双加氧酶(CatO_2ase)的促进作用和甘氨酸促使该酶分泌至胞外培养基中的作用.产酶量高低和分泌量多少与培养基种类、甘氨酸和L-异亮氨酸的浓度以及培养时间等因素有关.在甘氨酸存在的情况下,胞壁对溶菌酶的敏感性有所增加,超微形态似有变化,还存在其他物质的伴随分泌,故甘氨酸可能是引起细胞壁结构的改变而导致邻苯二酚2,3-双加氧酶等胞内容物被动分泌至胞外.     

0.7 MPa(7ATA)高气压下大鼠脊髓突触体甘氨酸摄取的变化

目的:研究氮麻醉时甘氨酸神经递质功能变化。方法:制备脊髓突触体,用同位素方法观察0.7MPa(7ATA)高压空气环境中大鼠脊髓突触体摄取甘氨酸的情况。结果:0.7MPa(7ATA)时甘氨酸摄取速度减慢,达到饱和摄取量时间延长,最大饱和摄取量下降。甘氨酸摄取的Vm减小,Km增加。在加入10-7mol.L-1皮质酮后,可增加0.7MPa(7ATA)高压空气时甘氨酸摄取Vm。结论:在高气压下发生氮麻醉时,甘氨酸摄取转运体的功能降低,与甘氨酸亲和力下降;皮质酮有助于高亲和力甘氨酸转运体功能恢复。     

不同晶型甘氨酸在水中溶解度的测定与关联

不同晶型甘氨酸溶解度的测定对研究甘氨酸结晶及多晶型现象具有重要意义。采用激光动态法测定了15~80℃范围内α型和γ型甘氨酸在纯水中的溶解度数据,并且采用Apelb lat溶解度经验方程对实验数据进行了关联,回归了溶解度经验方程的参数,关联效果令人满意。实验结果表明,在水中α和γ甘氨酸溶解度均随温度升高而变大;在相同温度下,热力学亚稳的α型甘氨酸比稳态的γ型甘氨酸溶解度大。     

Molecular biology of glycinergic neurotransmission

Glycine is a major inhibitory neurotransmitter in the spinal cord and brainstem of vertebrates. Glycine is accumulated into synaptic vesicles by a proton-coupled transport system and released to the synaptic cleft after depolarization of the presynaptic terminal. The inhibitory action of glycine is mediated by pentameric glycine receptors (GlyR) that belong to the ligand-gated ion channel superfamily. The synaptic action of glycine is terminated by two sodium- and chloride-coupled transporters, GLYT1 and GLYT2, located in the glial plasma membrane and in the presynaptic terminals, respectively. Dysfunction of inhibitory glycinergic neurotransmission is associated with several forms of inherited mammalian myoclonus. In addition, glycine could participate in excitatory neurotransmission by modulating the activity of the NMDA subtype of glutamate receptor. In this article, we discuss recent progress in our understanding of the molecular mechanisms that underlie the physiology and pathology of glycinergic neurotransmission.     

The Use of p‐Aminobenzoic Acid as a Probe Substance for the Targeted Profiling of Glycine Conjugation

Glycine conjugation facilitates the metabolism of toxic aromatic acids, capable of disrupting mitochondrial integrity. Owing to the high exposure to toxic substrates, characterization of individual glycine conjugation capacity, and its regulatory factors has become increasingly important. Aspirin and benzoate have been employed for this purpose; however, adverse reactions, aspirin intolerance, and Reye's syndrome in children are substantial drawbacks. The goal of this study was to investigate p‐aminobenzoic acid (PABA) as an alternative glycine conjugation probe. Ten human volunteers participated in a PABA challenge test, and p‐aminohippuric acid (PAHA), p‐acetamidobenzoic acid, and p‐acetamidohippuric acid were quantified in urine. The glycine N‐acyltransferase gene of the volunteers was also screened for two polymorphisms associated with normal and increased enzyme activity. All of the individuals were homozygous for increased enzyme activity, but excretion of PAHA varied significantly (16–56%, hippurate ratio). The intricacies of PABA metabolism revealed possible limiting factors and the potential of PABA as an indicator of Phase 0 biotransformation.     

Alpine plants show species-level differences in the uptake of organic and inorganic nitrogen

As an estimate of species-level differences in the capacity to take up different forms of N, we measured plant uptake of ¹⁵N-NH₄ ⁺, ¹⁵N-NO₃ ^– and ¹⁵N, [1]-¹³C glycine within a set of herbaceous species collected from three alpine community types. Plants grown from cuttings in the greenhouse showed similar growth responses to the three forms of N but varied in the capacity to take up NH₄ ⁺, NO₃ ^– and glycine. Glycine uptake ranged from approximately 42% to greater than 100% of NH₄ ⁺ uptake; however, four out of nine species showed significantly greater uptake of either NH₄ ⁺ or NO₃ ^– than of glycine. Relative concentrations of exchangeable N at the sites of plant collection did not correspond with patterns of N uptake among species; instead, species from the same community varied widely in the capacity to take up NH₄ ⁺, NO₃ ^–, and glycine, suggesting the potential for differentiation among species in resource (N) use.     

Autoradiographic localization of strychnine-sensitive glycine receptor in bovine adrenal medulla

The presence of an uptake system and a functional glycine receptor in adrenal medulla chromaffin cells was investigated using an autoradiographic technique in adrenal gland slices. Specific³[H]-glycine binding was observed in both adrenal cortex and medulla slices, while only specific binding of [³H]strychnine was seen only in chromaffin cells and was not associated with cortical cells. [³H]Glycine binding sites in the cortex are apparently different from those of [³H]strychnine binding sites in the medulla since excess strychnine does not displace [³H]glycine from adrenal cortex but does so from medulla. This difference supports biochemical evidence for glycine transport into medulla cells and glycine receptor sites on the chromaffin cell membrane.     

Glycine is taken up through GLYT1 and GLYT2 transporters into mouse spinal cord axon terminals and causes vesicular and carrier-mediated release of its proposed co-transmitter GABA

Glycine and GABA are likely co-transmitters in the spinal cord. Their possible interactions in presynaptic terminals have, however, not been investigated. We studied the effects of glycine on GABA release using superfused mouse spinal cord synaptosomes. Glycine concentration dependently elicited [(3)H]GABA release which was insensitive to strychnine or 5,7-dichlorokynurenic acid, but was Na(+) dependent and sensitive to the glycine uptake blocker glycyldodecylamide. The glycine effect was external Ca(2+) independent, but was reduced when intraterminal Ca(2+) was chelated with 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetracetic acid or depleted with thapsigargin, or when vesicular storage was impaired with bafilomycin. Glycine-induced [(3)H]GABA release was prevented, in part, by blocking GABA transport. The glycine effect was halved by sarcosine, a GLYT1 substrate/inhibitor, or by amoxapine, a GLYT2 blocker, and abolished by a mixture of the two. The sensitivity to sarcosine, used as a transporter inhibitor or substrate, persisted in synaptosomes prelabelled with [(3)H]GABA in the presence of beta-alanine, excluding major gliasome involvement. To conclude, in mice spinal cord, transporters for glycine (both GLYT1 and GLYT2) and for GABA coexist on the same axon terminals. Activation of the glycine transporters elicits GABA release, partly by internal Ca(2+)-dependent exocytosis and partly by transporter reversal.     

Glycine N-methyltransferases: a comparison of the crystal structures and kinetic properties of recombinant human, mouse and rat enzymes

Glycine N-methyltransferases (GNMTs) from three mammalian sources were compared with respect to their crystal structures and kinetic parameters. The crystal structure for the rat enzyme was published previously. Human and mouse GNMT were expressed in Escherichia coli in order to determine their crystal structures. Mouse GNMT was crystallized in two crystal forms, a monoclinic form and a tetragonal form. Comparison of the three structures reveals subtle differences, which may relate to the different kinetic properties of the enzymes. The flexible character of several loops surrounding the active site, along with an analysis of the active site boundaries, indicates that the observed conformations of human and mouse GNMTs are more open than that of the rat enzyme. There is an increase in kcat when going from rat to mouse to human, suggesting a correlation with the increased flexibility of some structural elements of the respective enzymes.     

Improvement of glycine biosynthesis from one-carbon compounds and ammonia catalyzed by the glycine cleavage system in vitro

Glycine cleavage system (GCS) plays a central role in one-carbon (C1) metabolism and receives increasing interest as a core part of the recently proposed reductive glycine pathway (rGlyP) for assimilation of CO₂ and formate. Despite decades of research, GCS has not yet been well understood and kinetic data are barely available. This is to a large degree because of the complexity of GCS, which is composed of four proteins (H, T, P, and L) and catalyzes reactions involving different substrates and cofactors. In vitro kinetics of reconstructed microbial multi-enzyme glycine cleavage/synthase system is desired to better implement rGlyP in microorganisms like Escherichia coli for the use of C1 resources. Here, we examined in vitro several factors that may affect the rate of glycine synthesis via the reverse GCS reaction. We found that the ratio of GCS component proteins has a direct influence on the rate of glycine synthesis, namely higher ratios of P protein and especially H protein to T and L proteins are favorable, and the carboxylation reaction catalyzed by P protein is a key step determining the glycine synthesis rate, whereas increasing the ratio of L protein to other GCS proteins does not have significant effect and the ratio of T protein to other GCS proteins should be kept low. The effect of substrate concentrations on glycine synthesis is quite complex, showing interdependence with the ratios of GCS component proteins. Furthermore, adding the reducing agent dithiothreitol to the reaction mixture not only results in great tolerance to high concentration of formaldehyde, but also increases the rate of glycine synthesis, probably due to its functions in activating P protein and taking up the role of L protein in the non-enzymatic reduction of H_ox to H_red. Moreover, the presence of some monovalent and divalent metal ions can have either positive or negative effect on the rate of glycine synthesis, depending on their type and their concentration.