DL-5-Hydroxytryptophan

This is a pyridoxal phosphate protein which catalyses the synthesis of serotonin. It may be assayed radiochemically using DL-5-hydroxytryptophan-l- C [447]. 

SYNS 5-HYDROXYTRYPTOPHAN ( )-5-HYDROXY-TRTTTOPHAN dl-5-HYDROXYTRYPTOPH.AN PRETONTNE... 

Substrate specificity of the purified indoleamine 2,3-dioxygenase from rabbit intestine was examined spectrophotometrically at 24°C. The spectra of the reaction products in either the absence or presence of formamidase were compared with those of authentic compounds. A single enzyme protein catalyzed the oxygenative ring cleavage of d- and L-tryptophan, 5-hydroxy-D- and -L-tryptophan, tryptamine, and serotonin (10). The maximal turnover number was obtained with L-tryptophan (99 mol min -mor of enzyme at 24°C), and the lowest value was with 5-hydroxy-L-tryp-tophan (20 p.Af). A marked substrate inhibition is observed by the L isomers of tryptophan and 5-hydroxytryptophan above 0.2 and 0.06 mM, at pH 6.6, respectively. The compounds including skatole, indole, in-doleacetic acid, 5-hydroxyindoleacetic acid, N-acetyltryptophan, melatonin, and a-methyl-DL-tryptophan, are all inert as substrate. 

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