A COMMENT ON THE H-1-NMR SPECTRA OF COBALT(II)-SUBSTITUTED SUPEROXIDE DISMUTASES WITH HISTIDINES DEUTERIATED IN THE EPSILON-1-POSITION

Erythrocyte superoxide dismutase Cu2Zn2SOD is a dimeric metalloenzyme containing one copper(II) and one zinc(II) ion bridged by a histidinato residue in each subunit. E2Co2SOD and Cu12Co2SOD are artificial derivatives of the native Cu2Zn2SOD1,2that permit the investigation through1H NMR spectroscopy of the protons of the cobalt domain.3,4Cobalt(II) is bound to three histidines and to one aspartate, as shown in the inset of Figure 1; each of the histidines is coordinated through its Nδ1nitrogen5: The1H NMR spectra of the bovine E2Co2SOD and Cu1Co2SOD derivatives are shown in Figure 1. In the Cu12Co2SOD derivative there are six sharp signals downfield; three of these (shaded in Figure 1) disappear when the spectrum is recorded in D2O. The latter are assigned as the N?2exchangeable protons of the three coordinated histidines. The other three signals are due to Hδ 2of the same histidines that are in a meta-like position with respect to the coordinating nitrogen.3Their T1| and line shape are consistent with signals assigned to meta-like protons of histidines in similar compounds.6-10In E2Co2SOD one NH signal is missing, probably because it exchanges rapidly on the NMR time scale. One or two broader signals are also present in the spectra, which were tentatively assigned to H?1 (ortho-like protons) of the above histidines because they are expected to be broader than the meta-like protons.4,11. © 1990, American Chemical Society. All rights reserved.