Fig. 8.
Scheme of the proposed metabolic interaction between neurons and astrocytes regarding glutathione synthesis. The GSH released from astrocytes is substrate for the astroglial ectoenzyme γGT. CysGly, one product of the γGT reaction, serves as a precursor of neuronal glutathione. It is not known whether the hydrolysis of CysGly occurs in the extracellular space by a neuronal ectopeptidase or after uptake of the dipeptide in the neurons. In addition, glutamine is released from astrocytes and used by neurons as precursor for glutamate necessary for glutathione synthesis. X represents an acceptor of the γ-glutamyl moiety transferred from glutathione by γGT, the most likely candidates being glutamine and H2O.