MEMBRANE-RECEPTOR FOR ODOR-BINDING PROTEINS

Specific binding of I-125-labelled bovine odour-binding protein (OBP) to isolated membranes from nasal mucosa was demonstrated. The interact ion reached equilibrium within 30 min at 37 degrees C and was reversib le. A Scatchard analysis of the equilibrium binding revealed a single population of binding sites, with the calculated equilibrium dissociat ion constant and maximum number of binding sites being 2.25+/-0.5 mu M and 18.5+/-2 pmol/mg of membrane protein respectively (n = 2). Recept or activity was decreased on digestion by trypsin, proteinase K or end oglycosidase H, was heat labile and was sensitive to thiol-group-speci fic reagents. With the exception of rat and mouse major urinary protei ns, which exhibit a high degree of structural similarity with OBP and bind similar ligands, other members of the lipocalin family, such as r etinol-binding protein and P-lactoglobulin, failed to inhibit the bind ing of I-125-labelled OBP to its receptor. The receptor seems not to b e 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 wi thin the body; possibilities include a role in detoxification or signa lling.