Glycine metabolism in animals and humans: implications for nutrition and health

• Published in: Amino acids Vol. 45; no. 3; pp. 463 - 477
• Main Authors: Wang, Weiwei, Wu, Zhenlong, Dai, Zhaolai, Yang, Ying, Wang, Junjun, Wu, Guoyao
• Format: Journal Article
• Language: English
• Published: Vienna Springer-Verlag 01.09.2013; Springer Vienna; Springer Nature B.V
• Subjects: absorption; Amino acids; ammonia; Analytical Chemistry; Animals; antioxidant activity; bile acids; Biochemical Engineering; Biochemistry; Biomedical and Life Sciences; biosynthesis; birds; cardiovascular diseases; choline; creatine; diabetes; dietary fat; digestion; glutathione; Glycine; Glycine - metabolism; glycine hydroxymethyltransferase; Health; heme; Humans; hydroxyproline; immunity; Injuries; Injury prevention; Invited Review; kidneys; Life Sciences; liver; long chain fatty acids; Mammals; Metabolism; neoplasms; Neurobiology; nucleic acids; Nutritional Requirements; obesity; Pathways; protein synthesis; Proteomics; serine; small intestine; swine; threonine; tissue repair; uric acid; Function; Synthesis; Nutrition; Glycine; Metabolism
• ISSN: 0939-4451; 1438-2199
• DOI: 10.1007/s00726-013-1493-1

Glycine is a major amino acid in mammals and other animals. It is synthesized from serine, threonine, choline, and hydroxyproline via inter-organ metabolism involving primarily the liver and kidneys. Under normal feeding conditions, glycine is not adequately synthesized in birds or in other animals, particularly in a diseased state. Glycine degradation occurs through three pathways: the glycine cleavage system (GCS), serine hydroxymethyltransferase, and conversion to glyoxylate by peroxisomal D-amino acid oxidase. Among these pathways, GCS is the major enzyme to initiate glycine degradation to form ammonia and CO₂in animals. In addition, glycine is utilized for the biosynthesis of glutathione, heme, creatine, nucleic acids, and uric acid. Furthermore, glycine is a significant component of bile acids secreted into the lumen of the small intestine that is necessary for the digestion of dietary fat and the absorption of long-chain fatty acids. Glycine plays an important role in metabolic regulation, anti-oxidative reactions, and neurological function. Thus, this nutrient has been used to: (1) prevent tissue injury; (2) enhance anti-oxidative capacity; (3) promote protein synthesis and wound healing; (4) improve immunity; and (5) treat metabolic disorders in obesity, diabetes, cardiovascular disease, ischemia-reperfusion injuries, cancers, and various inflammatory diseases. These multiple beneficial effects of glycine, coupled with its insufficient de novo synthesis, support the notion that it is a conditionally essential and also a functional amino acid for mammals (including pigs and humans).