Reactivity with Fe

Cyanide is a potent respiratory inhibitor that is much more reactive with Fe + than with Fe +. Thus, this reagent has compensated for CO, which lacks reactivity to Fe +, in studies of the function of the O2 reduction site, since the historical work of Keilin and Hartree (1938b) for identihcation of hemes a and as. However, cyanide is reactive also to ferrous iron although much more weakly than to ferric iron. Among... 

Azide very weakly perturbs the visible-Soret spectrum of the fuUy oxidized enzyme (Yoshikawa and Caughey, 1992, Li and Palmer, 1993). Azide has no reactivity with Fe +. Thus, in the presence of azide, heme a is preferentially reduced. The peak position of the hemochrome spectrum of heme a shifts from 601 nm in the absence of azide to 597 nm in the presence of azide at liquid N2 temperature. It was proposed that the spectral shift was due to azide binding to heme a (Gilmour et al., 1967). However, the spectral shift of heme a is probably induced by azide binding at heme aj. 

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