TIME-COURSE OF INHIBITION OF CELLULAR NUCLEIC-ACID SYNTHESIS BY SELENITE

The relationship between intracellular sulfhydryl (SH) compounds and t he kinetics of the inhibitory effect of selenite on cellular nucleic a cid synthesis has been examined. In A549 cells, with a relatively high SH level, exposure to low concentrations of selenite caused inhibitio n even after short exposure times. In contrast, in VA cells, with a re latively low level of SH compounds, selenite had no significant effect at short exposure times, but inhibited significantly with longer expo sures. Selenodicysteine, the product of the reaction of selenite with cysteine (an important intracellular SH compound), inhibited synthesis in both cell types at short exposure times. Exposure of cells to diet hylmaleate, which decreased the level of intracellular SH compounds, r educed the inhibitory effect of a short exposure to selenite but did n ot affect a long exposure. These results indicate that the reaction of selenite with intracellular SH compounds may be a determining factor in the kinetics of its inhibitory effect on cellular DNA and RNA synth esis.