Biochemical Properties of a Glutathione S-Transferase from the Onion Fly, Hylemya antiqua MEIGEN (Diptera : Anthomyiidae)

A glutathione S-transferase (GST) of the onion fly, Hylemya antiqua MEIGEN, was purified to apparent homogeneity by ammonium sulfate fractionation, anion exchange chromatography and glutathione-affinity chromatography. The enzyme was a homodimer of 50.0 kD with a subunit of 23.5 kD, and had an isoelectric point of 5.0. The bisubstrate reaction catalyzed by this enzyme followed a sequential mechanism rather than a ping-pong mechanism. Although the presence of other GST isozymes in the onion fly cannot be denied, the purified enzyme showed multiple functionality in addition to glutathione conjugation : bilirubin and hematin binding, and glutathione peroxidase activity.