Tryptophan metabolism in humans with various types of anemias.

S TUDIES OF TRYPOTOPHAN metabolism in man and animals with radioactively labeled compounds require a recognition of an inherent problem related to dosages employed if meaningful quantitative data are to be gathered and analyzed. Variations in amounts of tryptophan load used could account for the lack of a sound baseline for the evaluation of results obtained in different laboratories. In the past number of years it has been shown that tryptophan metabolite levels vary greatly in some disease categories.1 The level of tryptophan given to a patient may greatly affect the per cent of tryptophan metabolized to carbon dioxide. The observation that loading doses may significantly affect the per cent of the C14O2 excreted by a patient suggested that the loading dose with labeled tryptophan may be a test for deranged tryptophan metabolism regardless of the urinary excretion patterns.2 In previous studies2 we found that in a given individual, the results obtained from a single tracer dose without carrier differ significantly from those when a carrier dose of tryptophan ( 1 or 2 Gm. ) was given with the tracer dose. This procedure was chosen not as a quantitative measurement of metabolic pathways of physiologic levels of tryptophan, but rather with the thought that this method of approach might be helpful to the clinician in detecting aberrations in tryptophan metabolism in man. Price et al. in a review article emphasized that loading experiments could be useful in allowing the detection of abnormal metabolism, which might not be detected otherwise. It has been shown2 that the C14O2 production in man is a function of the loading dose given. With this fact in mind it was thought that the two gram loading dose combined with a tracer dose could be used to determine the severity of a disease. Tryptophan pyrrolase enzyme is an iron porphyrin ( apoenzyme ) which can be reconstituted with either heme or hematin with the latter being more associative than the former. A chemical reduction of hematin-enzyme yields