REDOX-SHIFT OF THE PHEROMONE-BINDING PROTEIN IN THE SILKMOTH ANTHERAEA-POLYPHEMUS

In pheromone-sensitive hairs of the male silkmoth Autheraea polyphemus , two electrophoretically distinct pheromone-binding proteins (PBPs) a re present. They indicate no amino acid sequence diversity according t o peptide mapping, but differ in their redox state, as shown by free-s ulfhydryl-group-specific cleavage at cysteine residues with 2-nitro-5- thiocyanobenzoic acid. In kinetic studies, the pheromone was initially bound mainly by the reduced PBP but later by the oxidized PBP, where all six cysteine residues form disulfide bonds. This redox shift was o bserved only in the homogenate of isolated olfactory hairs, where prot eins of the sensillum lymph and receptive dendrites are present. In co ntrol experiments with purified binding proteins, the proportion of ph eromone bound to the oxidized PBP did not increase with increasing inc ubation time, suggesting that disulfide formation does not occur spont aneously but is mediated by the sensory hairs, possibly by interaction with the receptor cell membrane. These data suggest that arriving hyd rophobic pheromone molecules are first bound by the reduced PBP and tr ansported through the aqueous sensillum lymph towards the receptor mol ecules of the dendritic membrane. The oxidized complex might not be ab le to activate further receptors and, thus, effectively deactivate the pheromone molecules within the sensillum lymph.