Reactions of oxy- and methemoglobin with tryptophan metabolites, 3-hydroxyanthranilic acid and 3-hydroxykynurenine.

It was found that 3-hydroxyanthranilic acid and 3-hydroxykynurenine have the capacity of oxidizing and reducing oxy- and met-hemoglobin. However, tryptophan metabolites such as kynurenine and anthranilic acid in which hydrxyl group is not involved did not oxidize and reduce these hemoglobins. The oxidation of oxyhemoglobin with 3-hydroxyanthranilic acid and 3-hydroxykynurenine was much accelerated in the presence of myo-inositol hexakisphosphate or superoxide dismutase, but was much suppressed in the presence of catalase. Deoxyhemoglobin was not oxidized by these compounds. On the other hand, the reduction of methemoglobin with 3-hydroxyanthranilic acid and 3-hydroxykynurenine proceeded both under aerobic and anaerobic conditions, though the rate of reduction was much faster under aerobic conditions than under anaerobic conditions. The reduction of methemoglobin with these compounds was accelerated by myo-inositol hexakisphosphate, but was partially suppressed by superoxide dismutase under aerobic conditions. On the basis of these results, the paradoxical effects of 3-hydroxyanthranilic acid and 3-hydroxykynurenine are discussed in relation to the mechanism of oxidation and reduction of hemoglobin.