Glyteine is a proprietary form of the dipeptide (small protein) gamma-glutamylcysteine, which is the immediate precursor to the tripeptide, glutathione.
Glutathione is synthesized in every cell of all oxygen using living organisms from bacteria, through to plants and animals. This synthesis is facilitated by two enzymes (biological catalysts). The first enzyme, glutamate cysteine ligase (GCL) joins the amino acids glutamate and cysteine together to form gamma-glutamylcysteine. The second enzyme, glutathione synthease (GS) adds the amino acid glycine to gamma-glutamylcysteine to form glutathione. Though gamma-glutamylcysteine is produced continuously in every cell of your body almost all of it is immediately converted to glutathione, so the gamma-glutamylcysteine content in your cells at any given time is almost negligible.