The effect of stress on the activity and level of mRNA of spermidine/spermine N1-acetyltransferase (SAT), a polyamine degradation rate-limiting enzyme, was studied in Ehrlich ascites tumor cells. When the cells were treated with sodium arsenite or ethanol for 1 h at 37 degrees C, the activity of SAT increased time- and dose-dependently. Total RNA was isolated from cells treated with stress, and the relative abundance of the SAT mRNA was measured by Northern blot analysis. The amount was comparable to those in control cells. In stress-treated cells, the biological half-life of the enzyme was 48-55 min, but 27-30 min in control cells. When cells were treated with arsenite in the presence of cycloheximide, enzyme activity did not increase. In those cells, half-life of the enzyme was shorter than in the cells treated with arsenite alone. This suggests that stress-treatment of cells enhanced SAT activity posttranslationally and that some factor(s) which was synthesized de novo during the treatment of arsenite is involved in the stabilization of the enzyme.