Evidence for Catechol Ring- Induced Conformational Restriction in Neurotransmitters

In the neurotransmission process, a specific neurotransmitter binds to a specific receptor in a “key and lock” recognition process. Neurotransmitters, such as the catecholamines, are flexible molecules that can change their shape easily in principle. However, conformations of both the “key” and “lock” must be quite limited to achieve high selectivity. We have investigated the conformational diversity of catecholamines and related molecules by laser spectroscopy. Molecules of the tyrosine family, which contain a phenolic aromatic chromophore, exist as several conformers. In contrast, a single conformer is observed in dopa and other catecholamines, which contain two hydroxyl groups on the benzene moiety (catechol). This demonstrates that the presence of a catechol ring restricts significantly the number of stable conformations.