Role of Odorant Binding Proteins: Comparing Hypothetical Mechanisms with Experimental Data

Abstract

Odorant binding proteins are expressed in the olfactory epithelium of many mammalian species and are thought to assist in the uptake and transfer of odorants from the gas phase to the odor receptors. Various mechanisms have been proposed to explain how mass transfer occurs. Most experimental work has focused on the binding of ligands to odorant binding proteins or to the olfactory receptors under steady-state conditions, whereas the situation in vivo is dynamic due to the tidal flow of air through the nose and the mass transfer in and out of the olfactory epithelium. Some preliminary dynamic data have been obtained from an in vitro system, and this has been used, along with other published data, to test some of the proposed mechanisms for odorant binding protein (OBP). An assessment of the hypothetical mechanisms has been made to examine how well the mechanisms fit with the published experimental data. A new hypothesis is proposed where OBP acts to prolong the odor signal and increases the signal output of the olfactory system.