ELECTRON-PARAMAGNETIC-RESONANCE SPECTRUM OF CRYSTALLINE JACK BEAN UREASE

X-band electron paramagnetic resonance (EPR) spectra of polycrystalline urease were recorded at room and liquid nitrogen temperatures. They are a superposition of narrow isotropic and broad anisotropic signals. Analysis of the spectra indicates that most Ni2+ ions in the enzyme interact in pairs (antiferromagnetic exchange coupling). The interactions cause deformation of ion coordination, which is reflected in the anisotropy of the EPR signal from Ni2+ ion pairs. The remaining Ni2+ ions, of nearly O(h) Coordination, are isolated.