METAL CHELATES IN THE STORAGE AND TRANSPORT OF NEUROTRANSMITTERS: INTERACTIONS OF Cu2+ WITH ATP AND BIOGENIC AMINES1,2

The thermodynamic stabilities of the coordinate binding of Cu2+ ion with adenosinetriphos‐phate (ATP) and several biogenic amines have been determined in aqueous model systems in an attempt to examine the possible correlation between metal‐amine binding and the in vivo affinities of the amines for granule‐binding. In each of the ternary chelate systems consisting of Cu2+‐ATP‐amine (1:1:1), the Cu2+ ion is preferentially bound by ATP in the pH range 3–5 with a stability constant of Log KML= 517. In the pH range 5–8 each of the biogenic amines coordinates with Cu2+ ‐ATP chelate to form the respective ternary chelate. The nature and strength of binding of fourteen different amines with Cu2+‐ATP have been evaluated on the basis of the stabilities of the ternary chelates. On the basis of the quantitative equilibrium data generated in this study, it appears that both pyrocatechol moiety and the ethanolamine side‐chain of the catechol amines are involved in the coordination of copper. The metal‐binding stabilities of the biogenic amines are then correlated with the molecular structure, donor basicities and the in vivo affinities of the amines for granule‐binding in order to rationalize the possible involvement of metal chelates in the monoamine binding, storage and transport.