NMR studies of plastocyanin have centered on the ligands to the copper atom at the active site, particularly histidines-37 and -87. Heteronuclear (13C, 1H) J-connectivity spectroscopy has enabled cross assignment of 1H and 13C NMR resonances from the two copper-ligated histidines. In addition to providing assignments of the 13C resonances, the two-dimensional Fourier transform NMR results require the reversal of the original 1H NMR assignments to the ring protons of histidine-37. The line widths of the ring protons of histidine-87 are field-dependent leading to determination of the reduced lifetime of the proton on the Nδ atom (about 400 μs).
