Tapiero H, Mathé G, Couvreur P, Tew K D
Faculté de pharmacie, Université de Paris, CNRS UMR 8612, 5, rue Jean-Baptiste-Clément, 94200 Chatenay-Malabry, France.
Biomed Pharmacother. 2002 Nov;56(9):446-57. doi: 10.1016/s0753-3322(02)00285-8.
Glutamine and glutamate with proline, histidine, arginine and ornithine, comprise 25% of the dietary amino acid intake and constitute the "glutamate family" of amino acids, which are disposed of through conversion to glutamate. Although glutamine has been classified as a nonessential amino acid, in major trauma, major surgery, sepsis, bone marrow transplantation, intense chemotherapy and radiotherapy, when its consumption exceeds its synthesis, it becomes a conditionally essential amino acid. In mammals the physiological levels of glutamine is 650 micromol/l and it is one of the most important substrate for ammoniagenesis in the gut and in the kidney due to its important role in the regulation of acid-base homeostasis. In cells, glutamine is a key link between carbon metabolism of carbohydrates and proteins and plays an important role in the growth of fibroblasts, lymphocytes and enterocytes. It improves nitrogen balance and preserves the concentration of glutamine in skeletal muscle. Deamidation of glutamine via glutaminase produces glutamate a precursor of gamma-amino butyric acid, a neurotransmission inhibitor. L-Glutamic acid is a ubiquitous amino acid present in many foods either in free form or in peptides and proteins. Animal protein may contain from 11 to 22% and plants protein as much as 40% glutamate by weight. The sodium salt of glutamic acid is added to several foods to enhance flavor. L-Glutamate is the most abundant free amino acid in brain and it is the major excitatory neurotransmitter of the vertebrate central nervous system. Most free L-glutamic acid in brain is derived from local synthesis from L-glutamine and Kreb's cycle intermediates. It clearly plays an important role in neuronal differentiation, migration and survival in the developing brain via facilitated Ca++ transport. Glutamate also plays a critical role in synaptic maintenance and plasticity. It contributes to learning and memory through use-dependent changes in synaptic efficacy and plays a role in the formation and function of the cytoskeleton. Glutamine via glutamate is converted to alpha-ketoglutarate, an integral component of the citric acid cycle. It is a component of the antioxidant glutathione and of the polyglutamated folic acid. The cyclization of glutamate produces proline, an amino acid important for synthesis of collagen and connective tissue. Our aim here is to review on some amino acids with high functional priority such as glutamine and to define their effective activity in human health and pathologies.
谷氨酰胺、谷氨酸与脯氨酸、组氨酸、精氨酸和鸟氨酸一起，占膳食氨基酸摄入量的25%，构成氨基酸的“谷氨酸家族”，它们通过转化为谷氨酸来代谢。虽然谷氨酰胺已被归类为非必需氨基酸，但在严重创伤、大手术、败血症、骨髓移植、强烈化疗和放疗时，当它的消耗量超过合成量时，它就变成了一种条件必需氨基酸。在哺乳动物中，谷氨酰胺的生理水平为650微摩尔/升，由于其在调节酸碱平衡中的重要作用，它是肠道和肾脏中氨生成的最重要底物之一。在细胞中，谷氨酰胺是碳水化合物和蛋白质碳代谢之间的关键环节，在成纤维细胞、淋巴细胞和肠细胞的生长中起重要作用。它能改善氮平衡并维持骨骼肌中谷氨酰胺的浓度。谷氨酰胺通过谷氨酰胺酶脱氨生成谷氨酸，谷氨酸是γ-氨基丁酸的前体，γ-氨基丁酸是一种神经传递抑制剂。L-谷氨酸是一种普遍存在的氨基酸，以游离形式或存在于肽和蛋白质中，存在于许多食物中。动物蛋白按重量计可能含有11%至22%的谷氨酸，植物蛋白中谷氨酸含量高达40%。谷氨酸钠被添加到几种食物中以增强风味。L-谷氨酸是大脑中最丰富的游离氨基酸，是脊椎动物中枢神经系统的主要兴奋性神经递质。大脑中大多数游离的L-谷氨酸来自L-谷氨酰胺和三羧酸循环中间产物的局部合成。它通过促进钙离子运输，在发育中的大脑神经元分化、迁移和存活中显然起着重要作用。谷氨酸在突触维持和可塑性方面也起着关键作用。它通过依赖于使用的突触效能变化促进学习和记忆，并在细胞骨架的形成和功能中发挥作用。谷氨酰胺通过谷氨酸转化为α-酮戊二酸，α-酮戊二酸是柠檬酸循环的一个组成部分。它是抗氧化剂谷胱甘肽和多聚谷氨酸化叶酸的组成部分。谷氨酸环化产生脯氨酸，脯氨酸是一种对胶原蛋白和结缔组织合成很重要的氨基酸。我们在此的目的是综述一些具有高度功能重要性的氨基酸，如谷氨酰胺，并确定它们在人类健康和疾病中的有效活性。
