Tryptophan binding to nuclei of rat liver and hepatoma

Abstract

This study was conducted to determine whether L-tryptophan binding to nuclei of rat transplantable hepatomas (5123 and 19) differed from that in host liver or normal liver of rats. Binding of L-tryptophan to rat hepatic nuclear proteins has been demonstrated to be saturable, stereospecific, and of high affinity and the nuclear envelope binding protein has been purified and characterized. Using an in vitro 3H-tryptophan binding assay, the total and specific L-tryptophan binding was appreciably less in nuclei of hepatoma than in nuclei of host liver or normal liver. On Scatchard analyses, the K D values were similar for nuclei of hepatoma and of host liver but the B max values were less in hepatoma than in host liver. Free L-tryptophan levels and nuclear poly(A)polymerase activity levels in hepatoma were higher than those of host liver. Using compounds (L-tryptophan implicated in the eosinophilia-myalgia syndrome, D,L-β-(1-naphthyl)alanine, chlordiazepoxide, and 3-methylindole) that had earlier been found to diminish in vitro 3H-tryptophan binding to rat hepatic nuclei, similar inhibitory effects were observed with nuclei of hepatoma or with nuclei of host liver. Using polyclonal antibodies raised against the L-tryptophan binding protein of rat hepatic nuclear envelopes, immunoblot assay was performed on nuclei of hepatoma and of normal liver. The receptor protein (67kD) was present in both preparations.