Biochemical Studies of Olfaction: Binding Specificity of Odorants to a Cilia Preparation from Rainbow Trout Olfactory Rosettes

Cilia isolated from the olfactory epithelium (olfactory rosettes) of rainbow trout (Salmo gairdneri) bind amino acids, which are odor stimuli to this species. We demonstrate that L-threonine, L-serine, and L-alanine bind to a common site, TSA, in the cilia preparation. All possible mixtures of two of the amino acids as competitors, with the third as the 3H-labeled ligand, were studied. The effect of two combined (unlabeled) competitors was always substantially less than additive compared with their actions singly. Along with additional inhibition studies using mixtures of inhibitors, the data show that the three odorants must interact with at least one common binding site, TSA. Binding of L-3H]lysine to site L was unaffected by addition of L-threonine, L-serine, or L-alanine, establishing its independence from site TSA. L-Arginine inhibited binding of L-3H]lysine, showing that both of these basic amino acids interact with site L. The data establish the presence, in trout olfactory cilia, of at least two separate and noninteracting populations of odorant binding sites, TSA and L.