Cyanide-ligated

Fig. 6. Mechanisms for the reduction of compounds I and II of HRP C by ferulic acid, after Henriksen et al. 195). This scheme is based on new information from the 1.45 A resolution crystal structure of the ternary complex of ferulic acid and cyanide-ligated HRP C 195). The direction of proton transfer is indicated by the dotted arrows. The mechanism is discussed in Section IV,B,2, and the crystal structure data in Section IV,F,4. Note that a distal site water molecule makes an important hydrogen bond with the backbone carbonyl group of Prol39 (a residue conserved in all members of the plant peroxidase superfamily).

Cyanide-ligated HRP C binds benzhydroxamic acid more weakly than the resting state enzyme, with values of 0.15 mM (50 mM potassium... 

The ternary complex of benzhydroxamic acid and cyanide-ligated HRP C is heterogenous to the extent that two binding modes can be detected by NMR (250,257). Their relative proportions are determined... 

The crystal structures of two ferulic acid complexes of HRP C have been solved, one with resting state enzyme (to 2.0 A resolution) and the other with the cyanide-ligated enzyme (to 1.45 A resolution) 195). These represent a major achievement for the crystallography of peroxidase complexes. The binary complex is heterogenous, according to the 2Fo-Fc omit difference electron density map of the active site. The disordered density observed has been interpreted in terms of three... 

The automated method differs from the ICSH method chiefly in that oxidation and ligation of heme iron occur after the hemes have been released from globin. Therefore, ferricyanide and cyanide need not diffuse into the hemoglobin and methemoglobin, respectively. Because diffusion is rate-limiting in this reaction sequence, the overall reaction time is reduced from approximately three minutes for the manual method to 3 —15 seconds for the automated method. Reaction sequences in the Coulter S + II and the Technicon H 1 and H 2 are similar. Moreover, similar reactions are used in the other Coulter systems and in the TOA and Unipath instmments. 

Pseudohalides of Se in which the role of halogen is played by cyanide, thiocyanate or selenocyanate are known and, in the case of Se are much more stable with respect to disproportionation than are the halides themselves. Examples are Se(CN)2, Se2(CN)2, Se(SeCN)2, Se(SCN)2, Se2(SCN)2. The selenocyanate ion SeCN is ambidentate like the thiocyanate ion, etc., p. 325), being capable of ligating to metal centres via either N or Se, as in the osmium(IV) complexes [OsCl5(NCSe)], [OsCl5(SeCN)], and trans-[OsCU(NCSe)(SeCN)]2-.920) Tellurium and polonium pseudohalogen analogues include Te(CN)2 and Po(CN)4 but have been much... 

This photochemical mode is observed in the case of electron-rich metal centres ligated by poor electron acceptors cyanide complexes, eg [Fen(CN),J4, [Run(CN)6]4 , [Moiv(CN)8]4, and [ WIV(CN)S]4 are known as the most efficient in the eMlv production. A typical reaction is photo-oxidation of hexacyanoferrate(II) ... 

Battistuzzi G, Bellei M, Borsari M et al (2005) Axial ligation and polypeptide matrix effects on the reduction potential of heme proteins probed on their cyanide adducts. J Biol Inorg Chem 10 643-651... 

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