Partial purification and characterization of glutathione S-transferase isozymes from the leaves of Juniperus communis, Larix decidua, and Taxus baccata.

Glutathione S-transferases (GST, EC 2.5.1.18) are dimeric enzymes capable to detoxify electrophilic xenobiotics in animals and plants. GST activity for the conjugation of several model compounds including CDNB and DCNB is constitutive in the needles of the coniferous species Juniperus communis, Larix decidua, and Taxus baccata. The enzyme activity was distributed throughout several enzyme isoforms. These isoenzymes could be separated and partially purified in a four step procedure to apparent homogeneity. In the needles of T. baccata, three GST isozymes were present, whereas in the needles of the other species four isoenzymes seemed to be constitutive. All enzymes exhibited acidic pls between 6.3 and 4.0 after isoelectric focusing. The subunit size of the isozymes was between 23 and 29 kD. Whereas GST from crops and weeds are thought to be predominantly homodimeric, we are able to demonstrate that larch and yew tree possess heterodimeric GST isoforms of 26 + 29 kD and 24 + 25 kD, respectively. The catalytic constants for GSH were low and comparable between enzymes and species, but the Km values for CDNB varied substantially. Larch GST was the only GST which showed activity against the potent GST inhibitor ethacrynic acid