The hypothesis that olfactory receptors are protein molecules is widely embraced. The objective of this research program is to test this hypothesis through affinity labeling of Schiff base-forming proteins in the olfactory epithelium of tiger salamanders (Ambystoma tigrinum). Correlation of chemical studies of pure proteins in vitro and behavioral studies in vivo has led to the theory that simple ketones form Schiff bases with receptor proteins in the course of their olfactory detection by this species. This theory of covalent attachment is testable, and this project is designed to test this theory by continuing the current collaboration between the organic chemistry laboratory at UCR and the behavioral laboratory at Monell. The strategy of this work involves three steps: experimental studies of covalent attachment in vitro (both with model proteins and with protein fractions isolated from the olfactory epithelium), statement of the implications of this chemistry with regard to the sense of smell, and in vivo testing of these implications using a behavioral assay with classically conditioned animals.
Specific aims of this project are as follows: (1) To develop a chemical assay for identifying affinity labeled fractions of the olfactory epithelium and to isolate covalently modified proteins; (2) To explore radioisotopic and fluorescence tagging of receptor sites; (3) To optimize the precision of olfactometric studies of Urodele behavior for the purpose of measuring olfactory thresholds, chemically induced selective anosmias, and chemical protection against covalent blockade of receptor sites; (4) To investigate dose-response relationships for chemical production of selective anosmia with respect to approximately 10 different odorants; (5) To correlate the time course of selective anosmia with levels of affinity labeling of Schiff base-forming proteins in the olfactory epithelium during the course of recovery from chemical treatment of the olfactory sacs of experimental animals.
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