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Articles

Regulation of Aromatic Amino Acid Biosynthesis in Higher Plants

I. Evidence for a Regulatory Form of Chorismate Mutase in Etiolated Mung Bean Seedlings ¹

^a Department of Plant Pathology, University of California, Davis, California 95616

Etiolated mung bean seedlings were examined for chorismate mutase activity. Evidence for the occurrence of two forms of the enzyme (designated CM-1 and CM-2) was obtained by ammonium sulfate fractionation, anion exchange cellulose chromatography, and isoelectric focusing. The two forms showed distinctly different properties, as CM-1 was inhibited by phenylalanine and tyrosine and activated by tryptophan, but inhibition by phenylalanine and tyrosine was reversed by tryptophan. The other form, CM-2, was unaffected by any of the three aromatic amino acids. Isoelectric points of the two forms were CM-1, pH 4.6, and CM-2, pH 5.6. The molecular weights estimated by molecular sieving on Sephadex G-200 were CM-1, 50,000, and CM-2, 36,000.

³ Present address: Department of Biochemistry, University of Nevada, Reno, Nev.

¹ This work was supported by Grant AI-06491 from the United States Public Health Service and by National Science Foundation Grant GB15396.