Biochemical studies of taste sensation—VIII. Partial characterization of alanine-binding taste receptor sites of catfish Ictalurus punctatus using mercurials, sulfhydryl reagents, trypsin and phospholipase C

Abstract

1. 1. Taste receptors for l-alanine in the channel catfish Ictalurus punctatus have been partially characterized. The binding activity, which is localized to a sedimentable fraction (Fraction P2), was assayed with l-[ 3H]alanine as the ligand. 2. 2. Addition of HgCl 2 or p- mercuribenzoate to the assay at 0.1–1 mM markedly inhibited binding. The effect was not reversible and was unaffected by increased l-alanine in the binding assay. 3. 3. The sulfhydryl reagents iodoacetate, 5,5′-dithiobis(2-nitrobenzoic acid), arsenite, and N- ethylmaleimide did not show appreciable inhibition of binding. The results suggest that the inhibitory effect of mercurials is not on specific sulfhydryl groups at alanine-binding sites. 4. 4. Treatment of Fraction P2 with phospholipase C decreased binding activity and treatment with trypsin led to increased binding activity.