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Tyrosine and phenylalanine ammonia lyases in Sporobolomyces roseus Camm, Edith Ellen

Abstract

The enzymes phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) were studied in the yeast Sporobolomyces roseus (Kluyver and van Neil). Cells grown on a glucose-salts medium were ground with alumina, and the cell-free buffer extract was fractionated with ammonium sulfate. Enzyme activity was assayed by measuring spectrophotometrically the cinnamic acid and p-coumaric acid produced from phenylalanine and tyrosine respectively. Further attempts at purification resulted in the inactivation of the TAL. Although the two enzymes were not separated by the purification procedures used, there is some evidence that the deamination of phenylalanine and tyrosine are catalyzed by different proteins, and not by a single enzyme with wide specificity. TAL appears to be precipitated by lower concentrations of ammonium sulfate than is PAL. The pH curves of the two enzymes are different. The specific activities of the two enzymes can be changed relative to one another in the cell by changing the medium upon which the cells were grown. The rates of production of the two enzymes vary independently during the growth of the cells. While the proteins are probably distinct, the production and activity of each enzyme seem to be under common control. Peak production of both enzymes occurs during late logarithmic-early stationary phase in the growth of a batch culture. Replacement media containing either phenylalanine or tyrosine stimulate the production of both PAL and TAL. Similarly, media containing cinnamic acid or p-coumaric acid repress the formation of the enzymes. Studies using labelled substrate show that both products inhibit the action of both enzymes.

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