A W-BAND ELECTRON-SPIN ECHO ENVELOPE MODULATION STUDY OF A SINGLE-CRYSTAL OF AZURIN

At 95 GHz, deep electron spin echo envelope modulations of ct single c rystal of the blue copper protein azurin have been observed. The modul ations arise from the coordinated nitrogens of the histidines that lig ate to copper. From the ESEEM frequencies, hyperfine and quadrupole te nsors of these nitrogens have been deduced. The isotropic hyperfine co upling of the copper-bound nitrogen of histidine-117 is 1.4 times larg er than that of histidine-46. The anisotropic hyperfine tensors show t hat the wave function of the unpaired electron on both coordinated nit rogens mainly concerns the sigma bonds with copper.