Alterations of the glutathione cycle enzymes during and after SV40-transformation of human fibroblasts.

The activities of several enzymes involved in the antioxidant system of the cell were studied in parallel to cytogenetic alterations at various times after SV40 infection and transformation of human fibroblasts. At early passages after SV40 infection, glutathione reductase (GSR), glutathione peroxidase (GPX), glutathione transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD) activities were decreased. This, associated with the low superoxide dismutase (SOD) and catalase activities previously noticed in these cells, suggested that they are in a highly pro-oxidant status. Although chromosomes carrying the genes encoding these enzymes are frequently underrepresented, there is no direct relationship between the number of chromosomes and enzyme activities. Except for GPX, all the activities tend to increase in established cell lines reaching levels comparable to those of non-transformed fibroblasts. The late increase of G6PD activity may correlate with the frequent duplication of the early replicating X. GSR seems to correlate with G6PD activity and GPX to SOD total activity. The most striking alterations affect mitochondrial and peroxisomal enzymes activities: SOD, GPX and catalase.