Magnetic dipole-dipole coupled Cu(II) pairs in nitric oxide-treated tyrosinase: a structural relationship between the active sites of tyrosinase and hemocyanin.
The T(r) and T[unk] states of tyrosinase were treated with NO. EPR spectra of the products observed at 14 degrees K and at 113 degrees 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 Deltam = 1 and Deltam = 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 degrees K and 14 degrees K ruled out significant exchange coupling between the ion pairs. The Deltam = 2 signals were not saturable up to 350 mW at 14 degrees K. The broad Deltam = 1 signals could be separated from accompanying signals by the saturation characteristics of the latter at about 10 mW at 14 degrees 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.
D001665:Binding Sites; D003386:Brachyura; D004156:Catechol Oxidase; D003300:Copper; D006433:Hemocyanins; D009682:Magnetic Resonance Spectroscopy; D009569:Nitric Oxide; D012908:Snails; D013329:Structure-Activity Relationship
D009569:Nitric Oxide; D003300:Copper; D006433:Hemocyanins; D004156:Catechol Oxidase