Glycine

– Needed as glutathione precursor

– Needed for SAM disposal

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Glycine is a nonessential amino acid with many important physiologic functions. It is one of three amino acids that make up glutathione. Glycine’s dietary sources include meat, fish, legumes, and gelatins.

Glycine is a major collagen and elastin component, which are the most abundant proteins in the body. Like taurine, it is an amino acid necessary for bile acid conjugation; therefore, it plays a key role in lipid digestion and absorption. [L] Glycine is the precursor to various important metabolites such as porphyrins, purines, heme, and creatine. It acts both as an inhibitory neurotransmitter in the CNS (via its interaction with strychnine-sensitive glycine receptors), and as an excitatory neurotransmitter on N-methyl-D-aspartate (NMDA) receptors. [L]

Glycine has anti-oxidant, anti-inflammatory, immunomodulatory and cytoprotective roles in all tissues. [L]

Supplementation with glycine has been used to ameliorate metabolic disorders in patients with obesity, diabetes, cardiovascular disease, ischemia-reperfusion injuries, inflammatory diseases, and cancers.99 Because of glycine’s excitatory effects on CNS NMDA receptors, research regarding the treatment of psychiatric disorders, such as schizophrenia, using glycine transport antagonists have shown great promise. [L]

Oral glycine can boost tissue levels of glutathione, especially with concurrent NAC and/or lipoic acid. Because glutathione levels decline during the aging process, supplementing with glycine can impact elderly patients with low protein intake. [L]

Glycine accepts a methyl-group from SAM to form sarcosine, using the enzyme glycine-N-methyltransferase (GNMT); therefore, sarcosine is methylated glycine. This conversion functions to control SAM excess, as is seen in excess methyl donor supplementation, SAM elevations due to adiposity/ obesity and general over-methylation.

In the folate cycle, glycine and serine are interconverted by the enzyme serine hydroxymethyltransferase (SHMT). Glycine accepts a methyl donor from 5-10 MTHF and becomes serine; therefore, serine is methylated glycine. These methyltransferase reactions and interconversions are readily reversible depending on the needs of the folate cycle to synthesize purines. [L]

Glycine can also be generated from choline, betaine, dimethylglycine, and sarcosine using the sarcosine dehydrogenase enzyme. [L]

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References:

- Wang W, Wu Z, Dai Z, Yang Y, Wang J, Wu G. Glycine metabolism in animals and humans: implications for nutrition and health. Amino acids. 2013;45(3):463-477. [L]

- Hashimoto K. Glycine transporter inhibitors as therapeutic agents for schizophrenia. Recent Pat CNS Drug Discov. 2006;1(1):43-53. [L]

- McCarty MF, O’Keefe JH, DiNicolantonio JJ. Dietary Glycine Is Rate-Limiting for Glutathione Synthesis and May Have Broad Potential for Health Protection. Ochsner J. 2018;18(1):81-87. [L]

- Amelio I, Cutruzzola F, Antonov A, Agostini M, Melino G. Serine and glycine metabolism in cancer. Trends Biochem Sci. 2014;39(4):191-198. [L]

- Locasale JW. Serine, glycine and one-carbon units: cancer metabolism in full circle. Nat Rev Cancer. 2013;13(8):572. [L]