The Biochemistry of Odorant Reception and Transduction

Odor reception and signal transduction have for some years represented the two major foci within the “molecular mechanisms of olfaction” group. Significant findings of the past decade allow us to view olfaction in a new light. We are finally beginning to see how the primary step of odor recognition really does work. This passage alone frees us to consider a more limited set of possibilities at more central levels. A significant debate has been peripheral vs. central. Does the peripheral nervous system, i.e. the primary receptor cells, have a dynamic role in determining how we perceive odor, or are the dynamic aspects of odor perception the restricted domain of the central nervous system, i.e. the brain? The specificity of peripheral receptors has always been recognized, however the nature of this specificity has been questioned. Is peripheral odor discrimination accomplished using many receptors, each with high specificity, or only a few receptors, each with relatively low specificity? In the extreme many-receptor case, each receptor is activated by a different molecular component of a complex mixture. With increased specificity, fewer distinct molecules can be detected. There are thus certain volatile molecules that can not be smelled, and the number of distinct receptors should reflect the number of molecules that can be smelled. In the extreme few-receptor case, each receptor is activated by a broad spectrum of different component molecules. With decreased specificity, more distinct molecules can be detected. All volatile molecules can be smelled, but not necessarily distinguished, and the number of distinct receptors should be far fewer than the number of molecules that can be smelled.