INDOLIC COMPOUNDS AFFECT TRYPTOPHAN BINDING TO RAT HEPATIC NUCLEI

This study evaluates the effects of indolic or indole-related compound s on binding of L-tryptophan (saturable, stereospecific and of high af finity) to rat hepatic nuclei or nuclear envelopes. Addition of any on e of many indolic or indole related compounds, and particularly of 3-m ethylindole, does not inhibit in vitro binding of [H-3]tryptophan to h epatic nuclear envelopes. However, when 3-methylindole (10(-10) to 10( -4) mol/L) is added in combination with unlabeled L-tryptophan (10(-4) mol/L), it diminishes the inhibitory effect of unlabeled L-tryptophan alone. Scatchard analysis of the binding affinities of in vitro [H-3] tryptophan binding to hepatic nuclear envelopes using L-tryptophan in the absence or presence of 3-methylindole reveals similar dissociation constants (K-D) under the two conditions, but the binding concentrati ons (B-max) were greater in the combined group compared with that in t he L-tryptophan alone group. Addition of 3-methylindole to liver befor e homogenization decreases specific [H-3]tryptophan binding to nuclei compared with controls (without addition). L-Tryptophan tube-fed to ra ts with or without 3-methylindole administration increases in vitro he patic protein synthesis compared with that of saline tube-fed controls . 3-Methylindole itself does not affect protein synthesis. Our report describes the effects of 3-methylindole on specific tryptophan binding to hepatic nuclear envelope receptor and discusses the possible impli cations thereof.