Effects of vitamins on hepatic nuclear binding of L-tryptophan

Summary. This study investigated the in vitro effects of selected vitamins on nuclear L-tryptophan receptor binding of rat liver. Our results revealed that some fat-soluble vitamins, β-carotene, retinyl acetate, calciferol, α-tocopherol, and Trolox, as well as some water-soluble vitamins, thiamine and riboflavin, acted to inhibit in vitro ³H-tryptophan binding to hepatic nuclei. On the other hand, pyridoxine had little or no effect. The addition of dithiothreitol, a protective agent for sulfhydryl groups, along with each vitamin decreased the vitamin's inhibitory effect on in vitro ³H-tryptophan binding to nuclei, with the exception of riboflavin and calciferol. The addition of L-leucine, which alone had no inhibitory effect on in vitro ³H-tryptophan binding to hepatic nuclei but when added with unlabeled L-tryptophan negated the effect of unlabeled L-tryptophan, caused a markedly diminished inhibitory binding effect due to each of the following vitamins, thiamine, β-carotene, retinyl acetate, and α-tocopherol and Trolox, but no effect on riboflavin and calciferol. Received December 29, 1999 Accepted March 8, 2000