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      Pheromone anosmia in a scarab beetle induced by in vivo inhibition of a pheromone-degrading enzyme

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      Proceedings of the National Academy of Sciences
      Proceedings of the National Academy of Sciences

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          Abstract

          Previous biochemical evidence suggests that a cytochrome P450 specific to male antennae of the pale-brown chafer, Phyllopertha diversa, has evolved as a pheromone-degrading enzyme. By using a bioinformatics approach, we have now cloned three P450 cDNAs: CYP4AW1, CYP4AW2, and CYP6AT1. RT-PCR indicated that CYP4AW2 is expressed in all tissues examined, that CYP6AT1 is antennae-rich, and that CYP4AW1 is antennae-specific. Both tissue specificity and electrophysiological studies strongly support that CYP4AW1 in P. diversa is a pheromone-degrading enzyme involved in pheromone inactivation. Highly sensitive, pheromone-specific olfactory receptor neurons in male antennae were completely desensitized by direct application of metyrapone into the sensillar lymph. When tested in the same or different individuals, the metyrapone treatment had no effect on olfactory receptor neurons tuned to the plant volatile (Z)-3-hexenyl acetate, which might be inactivated by an esterase. Metyrapone treatment did not affect pheromone reception in the Japanese beetle, Popillia japonica, in the scarab beetle, Anomala octiescostata, or in the Oriental beetle, Exomala orientalis. Metyrapone-induced anosmia was restricted to the pheromone detectors in P. diversa, which became insensitive to physiological concentrations of pheromones for a few minutes. As opposed to previous trials, the specificity of the inhibitor and pheromone system led to unambiguous evidence for the role of pheromone-degrading enzymes in the fast inactivation of pheromones.

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          Pheromone binding and inactivation by moth antennae

          The antennae of male silk moths are extremely sensitive to the female sex pheromone such that a male moth can find a female up to 4.5 km away. This remarkable sensitivity is due to both the morphological and biochemical design of these antennae. Along the branches of the plumose antennae are the sensilla trichodea, each consisting of a hollow cuticular hair containing two unbranched dendrites bathed in a fluid, the receptor lymph ,3. The dendrites and receptor lymph are isolated from the haemolymph by a barrier of epidermal cells which secreted the cuticular hair. Pheromone molecules are thought to diffuse down 100 A-wide pore tubules through the cuticular wall and across the receptor lymph space to receptors located in the dendritic membrane. To prevent the accumulation of residual stimulant and hence sensory adaptation, the pheromone molecules are subsequently inactivated in an apparent two-step process of rapid 'early inactivation' followed by much slower enzymatic degradation. The biochemistry involved in this sequence of events is largely unknown. We report here the identification of three proteins which interact with the pheromone of the wild silk moth Antheraea polyphemus: a pheromone-binding protein and a pheromone-degrading esterase, both uniquely located in the pheromone-sensitive sensilla; and a second esterase common to all cuticular tissues except the sensilla.
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            Spatial and temporal structures of pheromone plumes in fields and forests

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              Olfactory perireceptor and receptor events in moths: a kinetic model.

              A mathematical model of perireceptor and receptor events has been developed for olfactory sensilla on the antennae of the moth Antheraea polyphemus. The model includes the adsorptive uptake of pheromone molecules by the olfactory hair, their transport on and within the hair by diffusion, the formation of a complex of pheromone and the extracellular pheromone-binding protein (PBP), the interaction of the complex pheromone-PBP with the hypothetical receptor molecule on the plasma membrane of the olfactory cell, the deactivation of the pheromone and, finally, its enzymatic degradation. In the model the PBP with its reduced form (with one or two intramolecular disulfide bonds) first acts as a carrier of the odorant. Later, while the pheromone is bound, it changes to an oxidized form (three disulfide bonds) with a scavenger function (carrier-to-scavenger model). This process of pheromone deactivation rather than the enzymatic pheromone degradation is responsible for the fall of the receptor potential after stimulus offset. The model is based on morphometrical, radiometrical, electrophysiological and biochemical data reported by several authors. The study supports the idea that peripheral events rather than intracellular signalling processes govern the kinetics of the receptor potential in the unadapted receptor cell.
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                Author and article information

                Journal
                Proceedings of the National Academy of Sciences
                Proceedings of the National Academy of Sciences
                Proceedings of the National Academy of Sciences
                0027-8424
                1091-6490
                August 03 2004
                August 03 2004
                July 26 2004
                August 03 2004
                : 101
                : 31
                : 11459-11464
                Article
                10.1073/pnas.0403537101
                509178
                15277687
                2df43925-7ac4-4d3f-bcc6-f6ec0e9e26de
                © 2004
                History

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