Comparison of Cyanide and Carbon Monoxide as Ligands in Iron(II) Porphyrinates

摘要

Cyanide (CN~-) and carbon monoxide (CO) have long been of particular interest as classic inhibitors of respiration. CO competes with oxygen, binding to reduced iron (Fe~(2+)) to form the stable low-spin hemoprotein carbonyl complexes, whereas CN~- inhibits O2 reduction. GST is isoelectronic and isosteric with CO; both are linearly bound to heme centers, and their complexes can often be found with the same symmetries.'3' Unlike CO and O2, CNT binds to both iron(II) and iron(III) hemoproteins, leading in most cases, but not all, to low-spin states. The reaction of cyanide with ferrohemes has been relatively little-studied owing to the low stability of the complexes even at alkaline pH values (up to 9.4). In most hemoproteins, only the kinetics of cyanide dissociation has been investigated as a transient species during reduction of the ferric cyanide complex. The dissociation constants (K_(diss)) are of the order of 1 molL~(-1), compared to 10~(-4)-10~(-9) molL~(-1) in ferrihemes.