THE PRESENCE OF THIOLS IN THE HEPATIC NUCLEAR-BINDING SITE FOR L-TRYPTOPHAN - STUDIES WITH SELENITE

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