The activity of glutathione-S-transferases for five electrophilic substrates was measured in ten organs of the rat. Highest activity was found in the liver and steroidogenic organs. The activity in the heart, brain, spleen and lung was relatively low or nil for most substrates.

Phenotypically altered liver foci were produced in female Wistar rats by a single dose of N-nitrosomorpholine followed by promotion with phenobarbital (PB) for 20 or 28 weeks. Then treatment was changed to either hexachlorocyclohexane (HCH), or cyproterone acetate (CPA), or nafenopin (Naf) or clofibrate (Clof), two hypolipidemic drugs. Foci were identified by a positive reaction for gamma-glutamyl-transpeptidase (GGT) and other cytological markers. HCH and CPA could substitute for PB as foci promoters; in contrast, Naf and Clof decreased expression of GGT in foci resulting in a decline of number and area of detectable foci, effects particularly pronounced with Naf. Immunohistochemical investigations of serial sections revealed that Naf also reduced expression of the altered phenotype when cytochrome P450-PB and pyruvate kinase (type L) were used as foci markers, but not when glutathione-S-transferase B (GST-B) was used. Thus, the number of foci with enhanced GST-B did not decline significantly after the change from PB to Naf treatment. Furthermore, the reduction of GGT and the decrease of foci number during Naf treatment were not associated with increased evidence of cell death by apoptosis in foci, in contrast to the situation after PB withdrawal. These findings strongly suggest that the disappearance of GGT-positive foci after Naf is due to a phenotypic change resulting in a suppression of GGT expression rather than to physical elimination of foci.

From the matrix of rat liver mitochondria, three GSH transferases were isolated and named Transferase 1, 2.1 and 2.2. Transferases 1 and 2.2 were purified to electrophoretic homogeneity. Transferase 1 contributes up to about 90% of the total mitochondrial GSH-transferring activity. It has a molecular weight of approx. 45 000 and is composed of two subunits of similar size. The isoelectric point is at pH 7.1-7.4. The Km values for GSH and 1-chloro-2,4-dinitrobenzene are 0.3 and 0.7 mmol/l respectively. Transferase 2.2 has the same molecular weight and subunit structure like the Transferase 1 and an isoelectric point at pH 4.8. The apparent Km values for GSH and 1-chloro-2,4-dinitrobenzene are 0.3 mmol/l and 0.4 mmol/l respectively. Transferase 2.1 contributes only 1% of the total mitochondrial GSH-transferring activity. It has high apparent Km values for both GSH and 1-chloro-2,4-dinitrobenzene (5.6 mmol/l and 1.3 mmol/l resp.) and a limited spectrum of substrates.

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