Purification and characterization of tryptophan dioxygenase from Streptomyces parvulus.
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.
Hitchcock
M J
MJ
Department of Microbiology, Georgetown University School of Medicine, Washington, D.C. 20007.
Katz
E
E
D006418:Heme / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D013302:Streptomyces / Q000201:enzymology* / Q000254:growth & development; D013379:Substrate Specificity; D014364:Tryptophan / Q000031:analogs & derivatives; D014366:Tryptophan Oxygenase / Q000302:isolation & purification* / Q000378:metabolism
D006418:Heme; D014364:Tryptophan; D014366:Tryptophan Oxygenase