1. Enzyme activities involved in tryptophan metabolism along the kynurenine pathway in rabbits.
- Author
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Bertazzo A, Ragazzi E, Biasiolo M, Costa CV, and Allegri G
- Subjects
- 3-Hydroxyanthranilate 3,4-Dioxygenase, Animals, Carboxy-Lyases analysis, Hydrolases analysis, Indoleamine-Pyrrole 2,3,-Dioxygenase, Kynurenine 3-Monooxygenase, Male, Mixed Function Oxygenases analysis, Models, Chemical, Niacin metabolism, Oxygenases analysis, Picolinic Acids metabolism, Rabbits, Tryptophan blood, Tryptophan Oxygenase analysis, Dioxygenases, Intestines enzymology, Kidney enzymology, Kynurenine metabolism, Liver enzymology, Tryptophan metabolism
- Abstract
The following enzyme activities of the tryptophan-nicotinic acid pathway were studied in male New Zealand rabbits: liver tryptophan 2,3-dioxygenase, intestine indole 2,3-dioxygenase, liver and kidney kynurenine 3-monooxygenase, kynureninase, kynurenine-oxoglutarate transaminase, 3-hydroxyanthranilate 3,4-dioxygenase, and aminocarboxymuconate-semialdehyde decarboxylase. Intestine superoxide dismutase and serum tryptophan were also determined. Liver tryptophan 2,3-dioxygenase exists only as holoenzyme, but intestine indole 2,3-dioxygenase is very active and can be considered the key enzyme which determines how much tryptophan enters the kynurenine pathway also under physiological conditions. The elevated activity of indole 2,3-dioxygenase in the rabbit intestine could be related to the low activity of superoxide dismutase found in intestine. Kynurenine 3-monooxygenase appeared more active than kynurenine-oxoglutarate transaminase and kynureninase, suggesting that perhaps a major portion of kynurenine available from tryptophan may be metabolized to give 3-hydroxyanthranilic acid, the precursor of nicotinic acid. In fact, 3-hydroxyanthranilate 3,4-dioxygenase is much more active than the other previous enzymes of the kynurenine pathway. In the rabbit liver 3-hydroxyanthranilate 3,4-dioxygenase and aminocarboxymuconate-semialdehyde decarboxylase show similar activities, but in the kidney 3-hydroxyanthranilate 3,4-dioxygenase activity is almost double. These data suggest that in rabbit tryptophan is mainly metabolized along the kynurenine pathway. Therefore, the rabbit can also be a suitable model for studying tryptophan metabolism in pathological conditions.
- Published
- 2001
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