Membrane receptor for odour-binding proteins

Specific binding of ¹²⁵I-labelled bovine odour-binding protein (OBP) to isolated membranes from nasal mucosa was demonstrated. The interaction reached equilibrium within 30 min at 37 °C and was reversible. A Scatchard analysis of the equilibrium binding revealed a single population of binding sites, with the calculated equilibrium dissociation constant and maximum number of binding sites being 2.25±0.5 μM and 18.5±2 pmol/mg of membrane protein respectively (n = 2). Receptor activity was decreased on digestion by trypsin, proteinase K or endoglycosidase H, was heat labile and was sensitive to thiol-group-specific reagents. With the exception of rat and mouse major urinary proteins, which exhibit a high degree of structural similarity with OBP and bind similar ligands, other members of the lipocalin family, such as retinol-binding protein and β-lactoglobulin, failed to inhibit the binding of ¹²⁵I-labelled OBP to its receptor. The receptor seems not to be restricted to olfactory tissues, as it was detected in a variety of other tissues. This suggests that OBP is unlikely to play a role only in olfactory signal transduction. It might have a much broader role within the body; possibilities include a role in detoxification or signalling.