Abstract

Abstract
Caenorhabditis elegans globin GLB-26 (expressed from gene T22C1.2) has been studied in comparison with human
neuroglobin (Ngb) and cytoglobin (Cygb) for its electron transfer properties. GLB-26 exhibits no reversible binding for O2
and a relatively low CO affinity compared to myoglobin-like globins. These differences arise from its mechanism of gaseous
ligand binding since the heme iron of GLB-26 is strongly hexacoordinated in the absence of external ligands; the
replacement of this internal ligand, probably the E7 distal histidine, is required before binding of CO or O2 as for Ngb and
Cygb. Interestingly the ferrous bis-histidyl GLB-26 and Ngb, another strongly hexacoordinated globin, can transfer an
electron to cytochrome c (Cyt-c) at a high bimolecular rate, comparable to those of inter-protein electron transfer in
mitochondria. In addition, GLB-26 displays an unexpectedly rapid oxidation of the ferrous His-Fe-His complex without O2
actually binding to the iron atom, since the heme is oxidized by O2 faster than the time for distal histidine dissociation.
These efficient mechanisms for electron transfer could indicate a family of hexacoordinated globin which are functionally
different from that of pentacoordinated globins.