Pheromone deactivation catalyzed by receptor molecules: a quantitative kinetic model

A quantitative model of pheromone-receptor interaction and pheromonedeactivation, the supposed rate-limiting processes underlying the receptorpotential kinetics, is worked out for the moth Antheraea polyphemus. Inthis model, the pheromone interacts with the receptor molecule while boundto the reduced form of the pheromone binding protein. The receptormolecules--besides their receptor function-- catalyze the observed shift ofthe pheromone-binding protein from the reduced to the oxidized form(Ziegelberger, G., Eur. J. Biochem., 232, 706-711, 1995), which deactivatesthe pheromone bound to pheromone binding protein. With the followingparameters, the model fits morphological, radiometric, electrophysiologicaland biochemical data: a maximum estimate of 1.7 x 10(7) receptormolecules/cell (with 40,000 units/micron 2 of receptor cell membrane), rateconstants k1 = 0.2/(s.microM) for the association, k2 = 10/s for thedissociation of the ternary complex of binding protein, pheromone andreceptor, and k3 = 10/s for the deactivation via the redox shift. Withthese parameters, the duration of elementary receptor potentials elicitedby single pheromone molecules (approximately 50 ms) reflects the lifetimeof the ternary complex, tau = 1/(k2 + k3). The receptor occupancy producedby the model for threshold stimuli fits the sensitivity of the receptorcell to single pheromone molecules.