Possible presence of [3H]glutathione (GSH) binding sites in synaptic membranes from rat brain.

Reduced as well as oxidized forms of glutathione exhibited a significant displacement of the specific binding of [3H]L-glutamic acid (Glu), a potential candidate for the central excitatory neurotransmitter, to the rat brain synaptic membranes. In order to elucidate these findings, an attempt was made to determine whether or not the synaptic membranes contained the binding sites for this peptide using [3H]glutathione (GSH) as a ligand. The specific binding activity was detected in the synaptic membranous preparations and found to be dependent on the incubation temperature and incubation time. The binding reached a plateau within 60 min of incubation at 2 degrees C and 30 degrees C. [3H]GSH binding increased linearly with increasing concentrations of membranous proteins employed. Scatchard analysis revealed that the binding sites consisted of two separate independent components rather than being comprised of a single constituent. A significant and concentration-dependent displacement of the binding was induced not only by the addition of GSH, but also by the inclusion of some GSH derivatives without SH-moiety, such as the oxidized form of glutathione, S-methyl-glutathione and S-hexyl-glutathione. The binding was also significantly inhibited by various alpha- and gamma-peptides containing L-Glu, but not by those containing D-Glu. Amongst 4 different agonists and antagonists used for the subclassification of the central Glu receptors, an agonist, quisqualic acid, and an antagonist, 2-amino-4-phosphonobutyric acid, exhibited a significant inhibition of the binding at the highest concentration employed. These results suggest that the rat brain synaptic membranes may contain structure-selective, temperature-dependent, high affinity and saturable binding sites for glutathione.