Magnetic Dipole-Dipole Coupled Cu(II) Pairs in Nitric Oxide-Treated Tyrosinase: A Structural Relationship Between the Active Sites of Tyrosinase and Hemocyanin

AUTOR(ES)

Uiterkamp, A. J. M. Schoot

RESUMO

The Tr and T[unk] states of tyrosinase were treated with NO. EPR spectra of the products observed at 14°K and at 113°K showed mixtures of two signals. One had components in the region of g = 2, about 1200 G wide, and in the region of g = 4, showing hyperfine splitting. The other signal was similar to that arising from isolated Cu(II) ions in an axially symmetric environment. The first signal was indicative of Δm = 1 and Δm = 2 transitions arising from magnetic dipole-dipole coupled Cu(II) ion pairs. It closely resembled previously reported EPR spectra obtained from NO-treated hemocyanin, which were confirmed in this study. The normal Curie behavior of the signals between 230°K and 14°K ruled out significant exchange coupling between the ion pairs. The Δm = 2 signals were not saturable up to 350 mW at 14°K. The broad Δm = 1 signals could be separated from accompanying signals by the saturation characteristics of the latter at about 10 mW at 14°K. The results establish the presence of a pair of copper ions at the active site of tyrosinase, and a clsoe structural relationship between this active site and that of hemocyanin.

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