Glycine cleavage system: reaction mechanism, physiological significance, and hyperglycinemia
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- KIKUCHI Goro
- Tohoku University
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- MOTOKAWA Yutaro
- University of Tokushima
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- YOSHIDA Tadashi
- Yamagata University
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- HIRAGA Koichi
- Department of Biochemistry, University of Toyama Graduate School of Medicine and Pharmaceutical Sciences
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The glycine cleavage system catalyzes the following reversible reaction: <br>Glycine + H4folate + NAD+⇄5,10-methylene-H4folate + CO2 + NH3 + NADH + H+<br>The glycine cleavage system is widely distributed in animals, plants and bacteria and consists of three intrinsic and one common components: those are i) P-protein, a pyridoxal phosphate-containing protein, ii) T-protein, a protein required for the tetrahydrofolate-dependent reaction, iii) H-protein, a protein that carries the aminomethyl intermediate and then hydrogen through the prosthetic lipoyl moiety, and iv) L-protein, a common lipoamide dehydrogenase. In animals and plants, the proteins form an enzyme complex loosely associating with the mitochondrial inner membrane. In the enzymatic reaction, H-protein converts P-protein, which is by itself a potential α–amino acid decarboxylase, to an active enzyme, and also forms a complex with T-protein. In both glycine cleavage and synthesis, aminomethyl moiety bound to lipoic acid of H-protein represents the intermediate that is degraded to or can be formed from N5,N10-methylene-H4folate and ammonia by the action of T-protein. N5,N10-Methylene-H4folate is used for the biosynthesis of various cellular substances such as purines, thymidylate and methionine that is the major methyl group donor through S-adenosyl-methionine. This accounts for the physiological importance of the glycine cleavage system as the most prominent pathway in serine and glycine catabolism in various vertebrates including humans. Nonketotic hyperglycinemia, a congenital metabolic disorder in human infants, results from defective glycine cleavage activity. The majority of patients with nonketotic hyperglycinemia had lesions in the P-protein gene, whereas some had mutant T-protein genes. The only patient classified into the degenerative type of nonketotic hyperglycinemia had an H-protein devoid of the prosthetic lipoyl residue. The crystallography of normal T-protein as well as biochemical characterization of recombinants of the normal and mutant T-proteins confirmed why the mutant T-proteins had lost enzyme activity. Putative mechanisms of cellular injuries including those in the central nervous system of patients with nonketotic hyperglycinemia are discussed.<BR><BR>(Communicated by Tatsuo SUDA, M.J.A.)
収録刊行物
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- Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences
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Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences 84 (7), 246-263, 2008
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詳細情報 詳細情報について
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- CRID
- 1390001204145547904
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- NII論文ID
- 130000093931
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- NII書誌ID
- AA00785485
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- ISSN
- 13492896
- 03862208
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- NDL書誌ID
- 9646288
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- 本文言語コード
- en
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- データソース種別
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- JaLC
- NDL
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