Preliminary Characterization of Glutathione S-Transferases That Accumulate in Callus Cells of Pumpkin(Cucurbita maxima Duch.) : PROTEINS, ENZYMES AND METABOLISM

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Glutathione S-transferases (GSTs; EC 2.5.1.18) in sarcocarp tissue of pumpkin (Cucurbita maxima Duch.) fruit and in callus induced from the tissue were examined. The specific activity of GST in the callus was 6.9-fold higher than that in the tissue. The specific activity in the callus remained constant during cultivation. Column chromatography on DEAE-cellulose, hydroxylapatite, and S-hexylglutathione-agarose was used to fractionate soluble proteins that were precipitated by ammonium sulfate at 30% to 70% saturation from homogenates of the sarcocarp tissue of pumpkin fruit and the callus and GST activity was monitored. Two and seven isozymes of GST were identified in the tissue and in the callus, respectively. Furthermore, column chromatography on Sephadex G-200 and SDS-polyacrylamide gel electrophoresis, indicated that these GST isozymes were homo- and heterodimers of subunits of M_r 22,000 (Puga), and 23,000 (Pugb), 24,000 (Pugc) or 24,500 (Pugd). Puga and Pugb were predominant in the sarcocarp tissue and in the callus, respectively. Puga, Pugb, Pugc and Pugd had acidic pI values of 5.45, 5.00, 5.35 and 5.75, respectively. Rabbit antiserum against Pugb did not cross-react with the three other sub-units of GST during immunoblotting.
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