Glycine

The following presentation is based on that of Neurolab,¹, which has been supplemented and expanded.

Glycine is an inhibitory neurotransmitter and the smallest non-essential amino acid. Glycine is an important building block of almost all body proteins.²

Origin:
Glycine is absorbed through food or formed in the cell mitochondria from serine, threonine, choline and hydroxyproline.³

Dismantling:
Conversion of glycine by the enzymes serine aldolase and L-serine deaminase via serine to pyruvate. Decarboxylation of glycine with the lipoprotein lipoyllysine by glycine dehydrogenase.

Glycine is a component of acetylcholine and increases acetylcholine synthesis in the hippocampus, striatum and nucleus tractus solitarii.⁴

Effect of glycine:

• In the brain:
  • Comparable effect to GABA (inhibitory)⁵
    in addition
  • Agonist of glutamate NMDA receptors (exitatory)^{67 8}
    • Glycine is constantly present in low concentrations in the extracellular and cerebrospinal fluid. The concentration is generally sufficient to saturate the NMDA receptor.⁹
    • Glycine transporters can change the concentration locally⁹
  • High oral doses cross the blood-brain barrier⁸

Behavioral effects:

• Modulates the immune defense¹⁰
• Has an antioxidant effect¹¹¹⁰
  • Protects glutathione from degradation due to oxidative stress
• Has a cytoprotective effect¹⁰
• Modulates the sensation of pain
• Possibly improves memory, but not attention¹²
• Increases vasopressin, but not melatonin¹³
• High evening doses have a sleep-promoting and sleep-prolonging effect^{213 14}
  • In one case known to us of an adult woman with melancholic depression, glycine was able to remedy the massive sleep-through problems typical of melancholic depression.
• Anxiety-relieving
  • In the dorsal periaqueductal gray increasing anxiety⁷
• Improves schizophrenia symptoms permanently (even after cessation of glycation)⁸
  • Negative symptoms: effect size 0.8
  • Positive symptoms: effect size 0.5
  • Cognitive symptoms: effect size 0.4
  • Depressive symptoms: slight improvement