Glutathione

Glutathione (GSH) is a tripeptide of glutamate, cysteine, and glycine, supplied as a lyophilized powder for laboratory research use only. Almost all of the literature published under its name concerns the glutathione that cells make for themselves — the endogenous pool — which is a distinct subject from the exogenous tripeptide listed here.

The endogenous pool is assembled inside the cell in two ATP-dependent steps, by glutamate-cysteine ligase and then glutathione synthetase, and is partitioned across cytosolic, mitochondrial, and nuclear compartments by specific transport rather than by free diffusion. A concentration measured in any one compartment therefore reflects synthesis, consumption, and export within that compartment.

The intact tripeptide is not generally carried across the plasma membrane. Extracellular gamma-glutamyl transpeptidase cleaves it to its constituent amino acids, which are taken up and re-assembled inside the cell, so an exogenous molecule and the intracellular pool are linked by degradation and resynthesis rather than by direct transfer.

The availability literature is correspondingly mixed and route-dependent: a single large oral load of glutathione did not raise plasma concentration in a 1992 report, while dietary glutathione was described as absorbed intact in a 1990 rat study. Findings about endogenous status do not carry over to the exogenous compound unless that step is established separately.

Reported mechanism · literatureIn biochemistry glutathione is described as the principal low-molecular-weight thiol redox couple, cycling between its reduced (GSH) and disulfide (GSSG) forms and acting as cofactor for the glutathione peroxidase and glutathione S-transferase enzyme families. That description is of the endogenous pool, and is not a statement about the exogenous compound.