Nuclear magnetic resonance study of the exchangeable histidine protons in bovine and wheat germ superoxide dismutases.

Nuclear magnetic resonance studies at 220 MHz of the exchangeable histidine NH protons in bovine erythrocyte superoxide dismutase (BESOD) [EC 1.15.1.1] and the two isoenzymes of wheat germ superoxide dismutase (WGSODI and WGSODII) have been carried out. NMR spectral similarities reveal substantial structural homology of WGSOD with BESOD. Comparison of the spectra of the apoproteins and copper-free, native, and reduced proteins suggests that zinc has a structural role in WGSOD similar to that previously reported for BESOD [Lippard, S. J., Burger, A. R., Ugurbil, K., Pantoliano, M. W., & Valentine, J. S. (1977) Biochemistry 16, 1136]. Four resonances are assigned to conserved histidine residues, three of which are coordinated to the zinc atom while the fourth is nonligating.