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Infect Immun. 1973 October; 8(4): 604-611
Copyright © 1973 American Society for Microbiology. All Rights Reserved.

Distribution and Metabolism of ¹⁴C-Tryptophan in Normal and Endotoxin-Poisoned Mice

Department of Microbiology and Public Health, Michigan State University, East Lansing, Michigan 48823

ABSTRACT

DL-Tryptophan (benzene ring-¹⁴C) and its metabolites persist longer and in greater quantity in tissues of endotoxin-poisoned mice than in tissues of normal mice. Correspondingly less label is excreted in urine and feces and expired as ¹⁴CO₂ in the poisoned animals. The distribution of label (1.1 x 10⁶ dpm per microgram of tryptophan) was relatively constant whether it was administered alone or in combination with 20 mg of unlabeled L-tryptophan. Tryptophan must be metabolized through the tryptophan oxygenase pathway to be converted to carbon dioxide, but attempts to quantitatively correlate depressed tryptophan oxygenase activity with depressed carbon dioxide production were unsuccessful. It appears that neither tryptophan oxygenase nor substrate availability exclusively determine the quantity of tryptophan converted to ¹⁴CO₂ except under highly selected conditions. The validity of an earlier suggestion that expired ¹⁴CO₂ could be used to monitor in vivo tryptophan oxygenase activity is not supported by our data.