Glyteine (gamma glutamylcysteine) is the immediate precursor to glutathione. During ageing and in many chronic conditions, the affected cells lose the capacity to make enough gamma-glutamylcysteine to maintain sufficient levels of glutathione to fight off oxidative stress. Gamma-glutamylcysteine is synthesized by glutamate cysteine ligase (GCL) and it is unhealthy and permanent changes to this enzyme that results in the insufficient gamma-glutamylcysteine being produced.
Oral and injected glutathione supplements cannot theoretically overcome this deficiency within cells. Circulating glutathione cannot enter cells intact. It must be first broken down into its three amino acid components, glutamate, cysteine and glycine. Amino acids are the building blocks of proteins. This degradation process starts with an enzyme (gamma glutamyl transferase) which is on the outside surface (membrane) of most cell types.
Once the amino acids enter the cells, glutamate and cysteine feed into the damaged enzyme and as such cannot increase the amount of gamma-glutamylcysteine available for glutathione synthesis.
On the other hand, Glyteine can enter cells intact and once inside is converted to glutathione by the second synthesis enzyme, glutathione synthease. This provides Glyteine with the capacity to increase cellular levels above homeostasis. This may provide some transient relief to oxidative stress that may help cells affected by a damaged GCL recover and regain a healthy physiological function.