Effects of glutathione on the kinetics and structural properties of BbGSTP1-1 were investigated. The liganded state BbGSTP1-1 acquires the capacity to bind the hydrophobic molecules more avidly. Thus, GSH-binding produces significant conformational changes on BbGSTP1-1 which are transmitted to the hydrophobic binding site. Fluorescent experiments carried out with glutathione-analog S-methylglutathione suggest that the -SH group of tripeptide is essential for triggering protein conformational changes. It is argued that the capacity of BbGSTP1-1 to be modulated by GSH concentration allows it to play an efficient detoxication action in both aquatic and terrestrial environments.