Control of Actinomycin D Biosynthesis inStreptomyces parvullus: Regulation of Tryptophan Oxygenase Activity

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Abstract
Tryptophan oxygenase (tryptophan 2,3-dioxygenase; EC. 1.13.11.11) activity increases immediately before the initiation of actinomycin D production by S. parvullus. Whether this increase is due to a release from catabolite repression or the synthesis of an inducer substance was investigated. The standard culture medium (glutamic acid-histidine-fructose medium) used in antibiotic production studies with S. parvullus contains L-glutamate as a major constituent. L-Glutamate is almost totally consumed before the onset of actinomycin D synthesis. The addition of 10 mM L-glutamate at this stage completely abolished actinomycin D production and tryptophan oxygenase synthesis. Fourteen amino acids were tested for a similar effect. Of these, L-glutamate and L-aspartate had the most dramatic effect on tryptophan oxygenase and .beta.-galactosidase (.beta.-D-galactosidase), another inducible enzyme. Standard glutamic acid-histidine-fructose medium, preincubated for 23 h to remove L-glutamate, allowed the synthesis of actinomycin D and tryptophan oxygenase by cells at a stage of growth normally considered too early for antibiotic production. A chemically defined medium lacking L-glutamate and adjusted to pH 8.0 was designed to simulate the preincubation medium. The transfer of cells to this artificial preincubation medium resulted in the appearance of tryptophan oxygenase as early as 19 h before normal synthesis occurred, eliminating the possibility that an inducer molecule is synthesized and excreted during the preincubation period. The increase in tryptophan oxygenase activity before the onset of actinomycin D synthesis, and the synthesis of actinomycin D itself, is apparently due to a release from L-glutamate catabolite repression.

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