Antioxidant enzyme activities in normal and transformed mouse liver cells.

Copper- and zinc-containing superoxide dismutase (CuZnSOD), manganese-containing superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPX, both Se-dependent and Se-independent), and glutathione reductase (GR) were measured in normal, nitrosoguanidine-transformed and SV40-transformed mouse liver cells in culture, as well as in mouse liver homogenates. Enzyme activities were compared on the basis of 3 different endpoints: per mg protein, per mg DNA, and per 10(6) cells. Except for GR, activity of all the measured anti-oxidant enzymes was much higher in vivo than in vitro. All of the anti-oxidant enzyme activities were lower in general in the 2 transformed cell lines than in the in vitro normal cell line, except Cu-ZnSOD, which showed little change. However, MnSOD was the only enzyme which showed lowered activity in both transformed cell lines, no matter what endpoint was used. This finding is in agreement with previous work showing lowered MnSOD activity in tumor cells.