Comparative Investigation of Glutathione S-transferase (GST) in Different Crops and Purification of High Active GSTs from Onion (Allium cepa L.)

Glutathione S-transferases (GSTs; EC 2.5.1.18) are abundant proteins encoded by a highly divergent ancient gene family with protective functions through detoxification and non-catalytic roles as carriers of cytotoxins. In this work, we investigated the GST activities in seedlings of 38 crops to obtain a plant with high active GST for further study. In screening of 38 crops, onion seedling showed the highest GST activity (483.54 nmol min-1mg-1 protein) followed by wheat(372.89 nmol min-1mg-1 protein), barley (253.44 nmol min-1mg-1 protein), rice (244.12 nmol min-1mg-1 protein) and proso millet (173.34 nmol min-1mg-1 protein). Carrot seedling showed the lowest activity (3.63 nmol min-1mg-1 protein).In onion plants, both root and leaf showed high GST activity. Onion bulb GSTs were separated DEAE cellulose column chromatography, and purified by affinity chromatography (S-hexyl glutathione-agarose). Three GST peaks were found to elute at 67, 107 and 140mM of KCl gradient solution, and were named as GSTa, GSTb and GSTc. Among the three GSTs, GSTa, GSTb and GSTc contained 9.58, 61.45 and 28.97% of total activity, respectively. In purification, GSTa, GSTb and GSTc had specific activities of 9075, 17259 and 19868 nmol min-1 mg-1 protein, respectively, along with yield of 2.48, 3.17 and 1.28,and purification fold of 15.8, 29.9 and 34.5, respectively. The purity and molecular mass of the fraction was examined by SDS-PAGE. The silver staining of the purified GSTa, GSTb and GSTc indicated that final product of GSTb and GSTc were highly purified and migrated as a single band on SDS-PAGE with an apparent molecular mass of 27 kDa. However, GSTa eluted with Glyoxalase-I (Gly-I) and to purify GSTa, more methodological application are suggested.