15 - Molecular Mechanisms of Vertebrate Olfaction: Implications for Pheromone Biochemistry

Abstract

This chapter discusses the molecular mechanisms of vertebrate olfaction and implications for pheromone biochemistry. The concept of the olfactory transduction process postulates the existence of a protein receptor, probably a transmembrane protein, that interacts with a second messenger system, in all likelihood adenylate cyclase. The binding of the odorants to this receptor initiates the chain of events that eventually produces the firing of action potentials by the olfactory sensory neuron. Some authors have suggested that olfactory receptor proteins may not exist and that the interaction of odorants with the sensory cell is mediated by the lipid bilayer, as most odorants are lipophilic and readily enter the bilayer. This view is contradicted by a number of basic findings, which support the role of a protein receptor in olfactory transduction: (1) olfactory reception is affected by compounds that modify proteins, such as alkylating reagents, or by molecules that bind surface proteins, such as lectins; (2) the response to some odorants is stereospecific, and this fact cannot be accounted for by simple physical interactions with the membrane; (3) the fact that there are genetically determined specific anosmias in man, in other vertebrates, and in insects implies the involvement of gene products, that is, specific proteins, in the recognition process; (4) the involvement of adenylate cyclase in the transduction process implies the mediation of a protein receptor, as in many similar receptor systems.