Tryptophan Pyrrolase of Rabbit Intestine

Abstract 1. An enzyme that catalyzes the formation of formyl-d-kynurenine from d-tryptophan was purified about 100-fold from a homogenate of rabbit small intestine. Formyl-d-kynurenine thus produced was converted to d-kynurenine by formamidase present in rabbit intestine. 2. Methylene blue and ascorbic acid were required as cofactors. Xanthine oxidase with hypoxanthine could replace ascorbic acid, but hydrogen peroxide, added as such or enzymatically generated by glucose oxidase or l-amino acid oxidase, was not effective. Addition of catalase failed to inhibit the enzyme. 3. Several lines of evidence indicated the involvement of heme in the catalysis by the enzyme. An absorption spectrum characteristic of hemoprotein was observed in the purified active enzyme preparations. Inhibition by potassium cyanide or carbon monoxide was observed. The inhibition by carbon monoxide was reversed by illumination. 4. The purified enzyme could oxidize l-tryptophan as well as d-tryptophan. Kynurenine derived from l-tryptophan via formylkynurenine was identified as the l-isomer. Methylene blue and ascorbic acid were also required. A marked substrate inhibition was observed with l-tryptophan, but not with d-tryptophan.