The formation of hydrogen cyanide from histidine in the presence of amino acid oxidase and peroxidase

Abstract

Conditions were sought to increase the yield of HCN from l-histidine incubated with l-amino acid oxidase ( l-amino acid:oxygen oxidoreductase (deaminating), EC 1.4.3.2) from snake venom, and horseradish peroxidase (donor:hydrogen-peroxide oxidoreductase, EC 1.11.1.7). Small amounts of histidine and high buffer concentrations favored high HCN yields, which reached a maximum of 72%. Imidazole 4-aldehyde and imidazole 4-carboxylic acid were identified among the reaction products, together with CO 2, NH 3, H 2O 2 and imidazole acetic acid. The CO 2 formed was equal to the histidine oxidized, and to the sum of NH 3 plus HCN formed. The production of HCN was associated with an increased O 2 uptake, which was established from the beginning of the reaction, with no apparent lag and ranged from 1.2 to 1.6 μmol extra O 2 taken up/μmol HCN formed. The system was inhibited by catalase, but added superoxide dismutase caused a small stimulation of both HCN production and O 2 consumption, and a larger stimulation of H 2O 2 accumulation. Added hydroxylamine was cooxidized to nitrite in an amount equimolar with the HCN formed. This nitrite formation was inhibited by superoxide dismutase. The facts could be interpreted in terms of superoxide anion formation during the HCN-producing reaction.