Binding of the pheromonal steroid, 5α-androst-16-en-3-one, to membrane-enriched fractions of boar and rat olfactory epithelium; preliminary evidence for binding protein being a glycoprotein

Abstract A high degree of binding of 5α-[ 3 H ]-androstenone was recorded in membrane-enriched fractions of porcine olfactory tissue. The specific (i.e. high affinity, low capacity) binding had a mean K a approximately 2×10 8  M −1 . A Hill plot of the data showed a Hill coefficient of approximately 2, possibly suggesting co-operativity of binding, with binding constants increasing from 8×10 7 to 1.6×10 9  M −1 with increasing substrate concentration. The level of specific binding of 5α-[ 3 H ]-androstenone was nearly 10-fold higher than in corresponding respiratory tissue preparations and was markedly reduced in the presence of excess (approximately 1 μM) unlabelled 5α-androstenone. Corresponding fractions derived from rat olfactory tissue showed only 25% of the binding recorded for the pig. After incubation of 5α-[ 3 H ]-androstenone with solubilised olfactory cilial tissue (porcine), gel filtration and chromatography on a typical “glycoprotein” column (Concanavalin A-Sepharose B) were performed. Specific binding was recorded only in fractions corresponding to glycoproteins with M r of approximately 70–90 kDa. In a third series of experiments, fractions containing high concentrations of cilia, some still attached to the dendritic endings (as shown by electron microscopy) were obtained by a novel method involving stripping them off the nasal epithelium. The basal adenylate cyclase (AC) activity was very significantly ( P P