Ascorbate peroxidase cyanide

In addition to binding to cytochrome c oxidase, cyanide inhibits catalase, peroxidase, methemoglobin, hydroxocobalamin, phosphatase, tyrosinase, ascorbic acid oxidase, xanthine oxidase, and succinic dehydrogenase activities. These reactions may make contributions to the signs of cyanide toxicity (Ardelt et al. 1989 Rieders 1971). Signs of cyanide intoxication include an initial hyperpnea followed by dyspnea and then convulsions (Rieders 1971 Way 1984). These effects are due to initial stimulation of carotid and aortic bodies and effects on the central nervous system. Death is caused by respiratory collapse resulting from central nervous system toxicity. 

Besides using the bioactive agent to detect the ion of interest, another approach can include monitoring an ion by its inhibitory effect upon enzymatic activity. For example, horseradish peroxidase (HRP) can be immobilised onto one gate of a REFET [107] allowing the presence of cyanide ion to be measured at concentrations of 10 3-10 7 M. The approach used here is to monitor the inhibition of the enzymatic HRP effect, by the cyanide ion, on ascorbic acid. Even lower levels (10 10 M) of detection can be obtained using a polyphenol oxidase/clay composite immobilised on carbon, with no interference from chloride, nitrate or bromide [108]. 

Special conditions the above method is valid for a pure enzyme preparation, but cannot give entirely reliable measurements for impure samples. Interfering reactants in the medium may be allowed for by carrying out recovery experiments with a range of amounts of pure SOD added to the test enzyme preparation. Dialysis of the enzyme preparation will eliminate small molecules that may interfere, like ascorbate, reduced glutathione and catecholamines. The addition of 2 //M cyanide may be used to block peroxidases, which has only a minimal effect on the activity of Cu/Zn-SOD. Alternatively 10-5 M azide may be used to block peroxidases without effect on Cu/Zn-SOD. 

Floyd. R. A., Soong. L. M., and Culver, P. L. Horseradish peroxidase/ hydrogen peroxide-catalyzed oxidation of the carcinogen M-hydroxy-Af-acetyl-2-aminofluorene as affected by cyanide and ascorbate. Cancer Res.. 36 1510-1519.1976. 

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