Complexing of Copper Ion by Ergothioneine

Concurrent redox and complexation reactions between copper (II) and ergothioneine (ESH) have been investigated by means of optical, electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectra. An equimolar mixture of Cu (II) with ESH gave rise to a green complex. This complex showed an asymmetric peak at 675 nm assigned to d-d transition of Cu (II). The ESR spin Hamiltonian parameters (g =2.246, g =2.068, and A =158G) of the green complex were typical for the Cu (II) complex of sulfur coordination. In the presence of two molar or excess ESH to Cu (II), an yellow Cu (I) complex was formed. The result of 13C-NMR measurements supports that ESH also coordinates to Cu (I) ion through the thiolate sulfur in the yellow complex.