Cyanide hemin

Cyanide binding to the hydroxo complex of ferric hemes has been extensively studied in micellar solutions [15-17, 22, 34]. The binding of cyanide is found to be highly dependent on the pH and is maximum at pH 9.6. Optical spectral studies show a distinct isosbestic point at 412 nm for the formation of bis-cyano hemin in SDS from the hydroxo heme. The overall equilibrium is ... 

The activation energies calculated for the two steps of the above reaction are + 160 kJ/mol for the ki step and -l- 78 kJ/mol for the k2 step [15]. The overall enthalpy of reaction is — 78 kJ/mol. It has been found that the half-life for the ki reaction is sensitive to the counterion concentration in case of SDS micelles. The effect of added counterion may be due to the charge neutralisation of the sulphate anion heads in the SDS micellar Stern layer, to facilitate approach and penetration of the CN- ions at the micelle-water interface. Hemin encapsulated in CTAB micelles reacts much faster with cyanide compared to that in SDS presumably because of the cationic Stern layer in CTAB. The... 

In the presence of 0.25M cyanide (Table I), the rate of reaction was found to decrease markedly, except in the case of hemin. With that exception, the close correlation between rates of reaction in the presence of cyanide for simple salts and for metal porphyrins shows that... 

In particular, the H NMR spectra of the dichelated proto-hemin cyanide complexes reported by Traylor and Berzinis in 1980, which show eight methyl resonances ranging from 20.4 to 4.8 ppm at 35 °C in DMSO- 4, or from 30.2 to 3.7 ppm at 57 °C in DMF- /7, have been assigned by NOES Y/EXS Y, COSY, ROESY and DQF-COSY techniques and the nodal planes of the single imidazole ligand in the two isomers have been shown to lie at 100° and 170° counterclockwise of the x-axis of the hemes shown in Figure 14, bottom. Isomer... 

Another problem to be elucidated is the role of copper in cytochrome a. In the known copper enzymes such as tyrosinase and laccase, copper is an important component of the prosthetic group, but is released from the protein moiety by dialysis against potassium cyanide. In the case of cytochrome a, however, the mode of combination of copper must be different, since very little copper is released from the protein moiety by dialysis. The best known method of releasing the copper is by acid treatment. The role of copper in the electron trasnferring system is still obscure, though Cohen and Elvehjem (1934), Yoshikawa (1937), Schultze (1939, 1941), Gallagher et al. (1956), and Gubler et al. (1957) observed, from dietary experiments, that copper-deficient tissues and yeast have a low cytochrome oxidase activity and a decreased content of hemin a. 

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