Purification and characterization of tryptophan dioxygenase from Streptomyces parvulus |
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Authors: | M J Hitchcock E Katz |
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Institution: | Department of Microbiology, Georgetown University School of Medicine, Washington, D.C. 20007. |
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Abstract: | Tryptophan dioxygenase, derived from Streptomyces parvulus, was purified to near homogeneity and shown to have a native Mr of 88,000. Kinetic parameters of the enzyme were determined and evidence suggesting that it is a hemoprotein was obtained. Tryptophan dioxygenase has a high specificity toward L-tryptophan with an apparent Km of 0.3 mM. L-3-Hydroxykynurenine was a competitive inhibitor with respect to L-tryptophan with a Ki of 0.16 mM. In vitro, the enzyme displayed little activity in the absence of a reducing agent; ascorbate, at 50 mM, was the preferred reductant providing almost a 50-fold increase in enzyme activity. The regulation of tryptophan dioxygenase synthesis and activity is described. The expression of the enzyme is correlated with the biosynthesis of actinomycin D in S. parvulus. These results support the hypothesis that tryptophan dioxygenase functions as the first enzyme in the sequence converting L-tryptophan to the chromophore of this antibiotic. |
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