Degradation of histamine in the presence of ascorbic acid and Cu2+ ion; involvement of hydrogen peroxide.

In the presence, but not in the absence of Cu2+, ascorbate decomposes histamine in citrate phosphate buffer (pH 6.5) at 37 degrees, but not at 0 degrees. The breakdown is completely inhibited by catalase, but only slightly by superoxide dismutase, and scavengers of OH. like benzoic acid, ethanol or potassium iodide. A1 O2 scavenger, alpha-tocopherol also did not show significant effects on the reaction. On the other hand, addition of H2O2 to the reaction mixture markedly enhances the rate of histamine breakdown induced by ascorbate or ascorbate-Cu2+ systems. However, H2O2 alone cannot breakdown histamine even in the presence of Cu2+. Histamine breakdown induced by ascorbate appears to be dependent upon the autooxidation of this vitamin. From these results and the findings reported by Chatterjee et al. that the products of its aerobic oxidation, dehydroascorbic acid and H2O2 were ineffective in reacting with histamine in the presence of Cu2+, it is concluded that the combination of H2O2 and the intermediate of ascorbate oxidation (monodehydroascorbic acid or other unstable species), both of which are produced during the autooxidation of ascorbate, plays a major role in the histamine transformation by ascorbate-Cu2+ system.