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The Enzymic Synthesis of Chorismic and Prephenic Acids from 3-Enolpyruvylshikimic Acid 5-Phosphate

From the ¹ From the Department of Biochemistry, Columbia University, College of Physicians and Surgeons, New York, New York 10032

The conversion of 3-enolpyruvylshikimate 5-phosphate (I) to phenylpyruvate was studied in extracts of Escherichia coli. A separation and partial purification was achieved of the two enzymic activities concerned: chorismate synthetase which catalyzed the 1,4-conjugate elimination (E2') of orthophosphate from I to yield chorismic acid (II), and the enzyme complex catalyzing the reactions chorismate prephenate (III) phenylpyruvate.

Chorismate synthetase was inactive under aerobic conditions, and could be activated most effectively by a reduced flavin adenine dinucleotide-regenerating system in an atmosphere of H₂ or N₂. This was accomplished by the reduction of FAD with (a) reduced nicotinamide adenine dinucleotide and mammalian diaphorase or bacterial NADH dehydrogenase, or (b) platinum and H₂. Reduced riboflavin, FMNH₂, and platinum plus H₂ alone could replace FADH₂. Dithionite activated the enzyme with a short lag period. Sulfhydryl compounds were needed for maximal effect in these activation procedures, but were not indispensable.

Chorismate synthetase was activated slowly by NADH, or by thorough removal of oxygen, but only in the presence of thiols. The activation by NADH was probably due to trace amounts of flavins, since their removal abolished this effect. Preliminary evidence suggested that Fe⁺⁺ may be the labile component of the enzyme responsible for the sensitivity to oxygen, although added Fe⁺⁺ was also inhibitory.

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