The presence of thiols in the hepatic nuclear binding site for L-tryptophan: Studies with selenite

Abstract

This study investigated the effects in vitro of selenite and selenate on nuclear L-tryptophan receptors of rat liver. Sodium selenite at 10 −6M inhibited the in vitro 3H-tryptophan binding to rat liver nuclear receptors. No inhibitory effect of selenite on 3H-tryptophan binding to nuclear receptor was found in the presence of 10 −4M dithiothreitol, a protective agent for sulfhydryl groups. Selenate as well as sulfite or sulfate did not exert an inhibitory effect on the tryptophan receptor. The results based upon in vitro studies suggest that selenium in the form of selenite may reversibly affect the L-tryptophan binding at the sulfhydryl sites in the nuclear receptor protein. In vivo administration of high (toxic) levels of selenite before or along with L-tryptophan inhibited the L-tryptophan-induced stimulation of hepatic protein synthesis.