Biochemical characterization of independent olfactory receptor sites for 5'-AMP and taurine in the spiny lobster.

To understand the initial events in chemosensory transduction (i.e. binding of odorants to olfactory receptor sites), we have utilized a radioligand-receptor binding assay on a tissue preparation that is enriched in dendritic membrane from olfactory receptor cells in the spiny lobster Panulirus argus. Radioligands used were tritiated adenosine 5'-monophosphate (AMP) and taurine, which are two of the most excitatory compounds for spiny lobsters. Our results indicate the existence of two independent types of binding sites--a taurine binding site and an AMP binding site. For both the taurine and AMP binding sites, odorant binding is rapid, reversible, and saturable. KD values for the taurine and AMP binding sites are 2.3 and 2.0 microM, respectively, and Bmax values are 159 and 3.2 fmol/micrograms protein, respectively. The fact that the specificity, affinity, and independence of these two binding sites as defined in these biochemical studies are in agreement with those from electrophysiological studies suggests that these binding sites are olfactory receptor sites involved in sensory transduction.