GLYCINE CLEAVAGE SYSTEM - COMPOSITION, REACTION-MECHANISM, AND PHYSIOLOGICAL SIGNIFICANCE
GLYCINE CLEAVAGE SYSTEM - COMPOSITION, REACTION-MECHANISM, AND PHYSIOLOGICAL SIGNIFICANCE
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DOI：
10.1007/bf01659328
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发表时间：
1973-01-01
影响因子：
4.3
通讯作者：
KIKUCHI, G
中科院分区：
文献类型：
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作者：
KIKUCHI, G
甘氨酸裂解体系催化以下可逆反应：甘氨酸+四氢呋喃+NAD+⇌5，10-亚甲基-四氢呋喃+二氧化碳+NH3+NADH。甘氨酸裂解系统由四种蛋白质组分组成。这四种蛋白质最初以酶复合体的形式存在于肝脏线粒体中。以部分纯化的单个蛋白质组分为原料，详细研究了甘氨酸裂解和甘氨酸合成的部分反应。特别是可以分离到甘氨酸代谢的蛋白质结合中间体，并阐明了其性质和作用。提出了一个解释甘氨酸可逆裂解全过程的设想，甘氨酸裂解系统代表了包括哺乳动物、鸟类、爬行动物、两栖动物和鱼类在内的脊椎动物甘氨酸和丝氨酸分解的主要途径。丝氨酸在这些动物中的分解代谢主要是通过丝氨酸的裂解形成亚甲基四氢呋喃和甘氨酸，而不是通过丝氨酸脱水酶来脱氨。在尿素和氨基动物中，由甘氨酸的α碳和丝氨酸的β碳形成的亚甲基四氢呋喃在线粒体或组织中可被进一步氧化成二氧化碳，而在尿液动物中亚甲基四氢呋喃几乎不能被氧化成二氧化碳，而主要用于合成嘌呤。在动物中，甘氨酸裂解系统合成甘氨酸似乎没有明显的生理意义。
The glycine cleavage system catalyzes the following reversible reaction: Glycine + THF + NAD+⇌ 5,10-methylene-THF + + CO2+ NH3+ NADHReversibility of the overall reaction was established through the studies with the enzymes prepared from liver mitochondria of rat and cock and from extracts ofArthrobacter globiformisgrown on glycine. The glycine cleavage system is composed from four protein components. The four proteins were revealed to exist originally as an enzyme complex in the liver mitochondria. Partial reactions of glycine cleavage and glycine synthesis were studied in detail with partially purified individual protein components. Particularly a protein-bound intermediate of glycine metabolism could be isolated and its nature and role were clarified. A tentative scheme was presented to explain the whole process of the reversible glycine cleavage.The glycine cleavage system was shown to represent the major pathway of catabolism of both glycine and serine in vertebrates, including mammals, birds, reptiles, amphibians, and fishes. Serine catabolism in these animals proceeds mainly by way of the cleavage of serine to form methylene-THF and glycine rather than deamination by serine dehydratase. In ureotelic and ammonotelic animals methylene-THF formed from the α-carbon of glycine as well as theβ-carbon of serine could be further oxidized to CO2in either the mitochondria or the soluble tissue fractions, while in uricotelic animals methylene-THF could hardly be oxidized to CO2and instead, was utilized mostly for purine synthesis. Glycine synthesis by the glycine cleavage system did not appear to have appreciable physiological significance in animals.