Magnetic susceptibility studies of laccase and oxyhemocyanin.

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Abstract
The magnetic susceptibility of Rhus vernicifera laccase was remeasured over the temperature range 5-260.degree. K. In contrast to the previous results linear .times. vs. T-1 behavior was observed. The susceptibility of Limulus polyphemus oxyhemocyanin has also been measured in the range 5-260 .degree. K. Only weak paramagnetism, attributable to dissolved oxygen and a small amount of paramagnetic impurities, was observed. Analysis of the data establishes a lower limit of 550 cm-1 for J, consistent with the earlier work. The temperature dependence of the susceptibility of laccase is quantitatively accounted for by the presence of 2 paramagnetic Cu ions (types 1 and 2) per enzyme molecule. Curie law behavior at low temperatures rules out significant interaction between the 2 Cu types, indicating that these redox centers are well separated (several angstroms) and are not connected by bridging ligands. Formulation of the type 2 site as binuclear Cu(II) requires J .gtoreq. 500 cm-1.