Effect of orally administered tryptophan pyrrolase activity in ovine and bovine

Abstract A major pathway of tryptophan metabolism is through kynurenine. There are two enzymes known to be involved in the conversion of tryptophan to kynurenine. Tryptophan pyrrolase mediates the cleavage of the pyrrole moiety of tryptophan. The product of this reaction, formylknurenine, is converted to kynurenine through mediation of kynurenine formamidase (formylase). Knox and Mehler 1 found the latter enzyme to be in 600-fold excess in liver preparations and indicated that any change in kynurenine formation was therefore due to activity of the pyrrolase. It has been shown repeatedly that there is an increased conversion of tryptophan to kynurenine upon administration of tryptophan, indicating an adaptive increase in the tryptophan pyrrolase. Tryptophan pyrrolase adaptation has been demonstrated in monogastric animals (rat, rabbit, and guinea pigs); but this phenomenon has not been reported in the ruminant. The experiments herein reported were designed to determine whether oral tryptophan would induce tryptophan pyrrolase activity in the ovine and bovine.