Utilization of dietary tryptophan in iron-deficient rats.

Excretion of urinary tryptophan in iron-deficient rats increased threefold while the excretion of N-methyl nicotinamide, a catabolic product of tryptophan, decreased by one-half compared to control rats. The activity of hepatic tryptophan oxygenase, the first enzyme of tryptophan metabolism, was not affected by iron deficiency. It is concluded that tryptophan supplementation in severe iron deficiency would not be beneficial.