Possible Participation of Superoxide Anion in the Intestinal Tryptophan 2,3-Dioxygenase Reaction

Highly purified preparations of superoxide dismutase obtained from bovine erythrocytes and green peas inhibited the catalytic activity of intestinal tryptophan 2,3-dioxygenase at any stage of reaction. On the contrary, superoxide dismutase failed to inhibit hepatic and pseudomonad tryptophan 2,3-dioxygenases during the steady state of reaction. With hepatic and pseudomonad enzymes, however, a prolonged lag period was observed when dismutase was added to the reaction mixture prior to the start of reaction. Further experiments with superoxide anion, produced by electrolytic reduction of molecular oxygen, indicated that superoxide anion may be involved in the catalytic mechanism of intestinal enzyme while it reductively activates pseudomonad and hepatic enzymes.