TRYPTOPHAN BINDING TO NUCLEI OF RAT-BRAIN

Nuclei purified from whole rat brain specifically bind [3H]tryptophan ([3H]Trp) under in vitro conditions. Excess unlabeled Trp (10-4 M) is an effective inhibitor of in vitro [3H]Trp binding to brain nuclei. Rats tube-fed l-tryptophan (Trp) ( 30 mg 100 g body wt) 30 min to 4 hr before killing revealed decreased specific binding of [3H]Trp to purified brain nuclei in vitro. By Scatchard analysis, the nuclei from whole brain appear to contain one binding site for [3H]Trp, and the KD is 263 nM. A number of Trp-related compounds, Trp metabolites, or other amino acids and their analogues were observed to compete for in vitro [3H]Trp binding to brain nuclei. The ability of Trp analogues, metabolites, and other cognate compounds to inhibit in vitro [3H]Trp binding to brain nuclei was evaluated and utilized to map the active site of Trp binding. © 1992.