Organ distribution and kinetics of Glutathione transferase from African river prawn, Macrobrachium vollenhovenii (Herklots)

The distribution of glutathione transferase (GST) in the major organs of African river prawn (Macrobrachium vollenhovenii) was studied. All the organs studied had GST activity. The specific activity of the extract from the hepatopancreas was highest while that from the muscle lowest. Purified GST from the hepatopancreas which could conjugate glutathione (GSH) with only 1-chloro-2,4-dinitrobenzene (CDNB) and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBDCl) among some electrophilic substrates tested, had a KmNBDCl of 2.2 ± 0.12 mmol l−1 while the KmCDNB was 2.03 ± 0.29 mmol l−1. Chloride ion, a product of the enzymatic reaction readily inhibited the conjugation of CDNB with GSH with an I50 of 0.12 mmol l−1, whereas chloride ion up to 0.6 mol l−1 had no inhibitory effect on the conjugation of GSH with NBDCl. However, nitrite inhibited the two reactions but the Ki for the conjugation of NBDCl was lower than the Ki for the conjugation of CDNB. The enzyme had an optimum temperature of 40 °C and an activation energy of 35.1 kJ/mol. The overall results show that M. vollenhovenii GST (mvGST) uses different mechanisms for different electrophilic substrates. The high Km of mvGST for the electrophilic substrates may be a special physiological adaptation for effective xenobiotic detoxication.