BACnEIUOLOGICAL REVIEWS, Dec. 1968, p. 465-492 Vol. 32, No. 4, Pt. 2 Copyright © 1968 American Society for Microbiology Printed in U.S.A. Pathways of Biosynthesis of Aromatic Amino Acids and Vitamins and Their Control in Microorganisms FRANK GIBSON AND JAMES PITTARD John Curtin School of Medical Research, Australian National University, Canberra, Australia, and School of Microbiology, University of Melbourne, Australia INTRODUCTION................................................................ 465 INTERMEDIATES IN AROMATIC BIOsYNTHESIS ...................................... 466 Common Pathway ........................................................... 466 Tryptophan Pathway ........................................................ 468 Pathways to Phenylalanine and Tyrosine ........................................ 469 Pathway to 4-Aminobenzoic Acid.............................................. 469 Intermediates in Ubiquinone Biosynthesis ....................................... 470 Intermediates in Vitamin K Biosynthesis ........................................ 471 Pathways Involving 2,3-Dihydroxybenzoate ..................................... 472 Other Phenolic Growth Factors ............................................... 473 ISOENZYMES AND PROTEIN AGGREGATES CONCERNED IN AROMATIC BiosYNTHESIS ........ 474 Common Pathway ........................................................... 474 Tryptophan Pathway ......................................................... 474 Phenylalanine and Tyrosine Pathways .......................................... 475 REGULATION OF THE COMMON PATHWAY ........................................ 476 Feedback Inhibition of DAHP Synthetase ....................................... 477 Repression of DAHP Synthetase .............................................. 478 Inhibition of Other Enzymes of the Common Pathway ............................ 480 Repression of Other Enzymes of the Common Pathway ........................... 480 REGULATION OF THE TRYPTOPHAN PATHwAY ..................................... 481 Feedback Inhibition .......................................................... 481 Repression................................................................. 481 REGULATION OF THE TYROSINE PATHWAY ........................................ 482 Feedback Inhibition .......................................................... 482 Repression................................................................. 482 REGULATION OF THE PHENYLALANINE PATHWAY .................................. 483 Feedback Inhibition .......................................................... 483 Repression................................................................. 483 REGULATION OF THE PATHWAYS OF VITAMIN BIOSYNTHESIS ............................ 483 CHROMOSOMAL DISTRIBUTION OF GENES CONCERNED wrTH AROMATIC BIOSYNTHEsI......s 484 CONCLUSION.................................................................. 485 LITERATURE CITED ............................................................ 486 INTRODUCTION and control of the biosynthesis of aromatic The aims ofthis review are to present an outline amino acids has accumulated. In addition, the of the metabolic pathways leading to the aromatic general outlines of the pathways leading to the amino acids and vitamins and to discuss how metabolically important compounds found in the flow of intermediates along these pathways is small amounts, namely, 4-aminobenzoic acid, controlled. The general outlines of the pathways ubiquinone, vitamin K, and 2, 3-dihydroxy- to the aromatic amino acids, phenylalanine, benzoic acid, are partially understood. The tyrosine, and tryptophan have been known for latter compounds will be referred to as vitamins. some time, and they were excellently reviewed It is these more recent studies which we intend by Umbarger and Davis (162). Since then, the to emphasize with one important exception, the situation regarding the "branch points" in tryptophan operon. The biochemical genetics of aromatic biosynthesis has been clarified, and this operon as a whole, and the enzyme trypto- much information on the biochemical genetics phan synthetase in particular, have been studied 465 466 GIBSON AND PITIARD BACTERIOL. Rev. intensively during recent years. The amount of INTERMEDIATES IN AROMATIC BIosYNTHEsIs information now available on these topics war- rants a separate review; therefore, it is not our Common Pathway intention to deal with this work in detail. Various The common pathway involves the condensa- aspects of the work have been reviewed (171, tion of two products of carbohydrate metabolism, 172); other recent general reviews on aromatic phosphoenolpyruvate and erythrose 4-phosphate, biosynthesis generally, or on specific topics, are to give a straight chain seven-carbon compound also available (12, 48). There has been, of neces- which is then cyclized and undergoes a num- sity, some selection in the papers cited, but ber of reactions through shikimate to chorismate further references may readily be found through (Fig. 2). these. In recent work, the main advance has been the A general outline of the pathways to be dis- clarification of the region of the branch point cussed consists of a "common pathway" leading (Fig. 1) where, from chorismate, a series of through shikimate to chorismate, after which individual pathways diverge. After the establish- there is branching to the individual pathways ment of 3-enolpyruvylshikimate 5-phosphate as (Fig. 1). an intermediate on the common pathway (101, PHENYLAILANINE TYROSINE TRYPTOPHAN ERYTHROSE __ 4-PHOSPHATE GLUCOSE + i CHORISMATE _ 4-AMINOBENZOATE __ FOLATE 4 PHOSPHOENOL- "Common pathway" PYRUVATE through shikimate 2,3-DIHYDROXYBENZOATE UBIQUINONE VITAMIN K 2,3-DIHYDROXYBENZOYLSERINE FIG. 1. General outline ofpathwaysfor theformation ofaromatic amino acids and vitamins in E. coli. PEP COOH COOH I C-O-P03H2 I II c=o CH2 CH2 HO COOH-H2 NADPH HO-C-H 3 CHO I I 2 3 CH--OHI H-C-OH OH H-C-OH I OH I~rO-po3H2 H-C-OH OH H-C-OH I DHS SA H2 DHQ CHr-O-po3H2 Ct-OH EP DAHP COOH COOH COOH PEP CH -H3P04 CH H OP-Ok )OH6 H2OP-0 0-C L O-t OH OH COOH OH COOK SAP EPSAP CA FIG. 2. Intermediates in the common pathway of aromatic biosynthesis. Abbreviations: PEP, phosphoenolpyru- vate; EP, erythrose 4-phosphate; DAHP, 3-deoxy-D-arabino-heptulosonic acid 7-phosphate; DHQ, 5-dehy- droquinic acid; DHS, 5-dehydroshikimic acid; SA, shikimic acid; SAP, shikimic acid 5-phosphate; EPSAP, 3-enolpyruvylshikimic acid 5-phosphate; CA, chorismic acid. Trivial names of enzymes and some references to purification and cofactors:- (1), 3-deoxy-D-arabino-heptulosonate 7-phosphate synthetase (DAHP synthetase; 48, 154, 164); (2), 5-dehydroquinate synthetase (153); (3), dehydroshikimate reductase; (4), shikimate kinase; (5), 3-enolpyruvylshikimnate 5-phosphate synthetase (102); (6), chorismate synthetase (119). VOL. 32, 1968 AROMATIC BIOSYNTHESIS 467 102), two groups studying the conversion of reaction of the common pathway) of Escherichia shikimate to anthranilate showed that 3-enol- coli was tested. The concentration of 4-amino- pyruvylshikimate 5-phosphate was a precursor of benzoate required for half-maximal growth of anthranilate, as well as of phenylpyruvate and such an auxotroph is about 10" M, but the addi- 4-hydroxyphenylpyruvate (73, 138). It was tion of a large excess of chorismate (5 X 10-4 M) suggested that a specific branch point compound did not support growth. The addition of dimethyl- was involved, and this compound was sought by sulfoxide (5%), which has been shown to examining a mutant in which the pathways to increase cellular permeability (61), did not affect tryptophan, tyrosine, and phenylalanine were the results. blocked (71, 72). The instability of chorismate and its inability Using ultraviolet irradiation followed by to promote growth probably were factors in the penicillin selection, a strain requiring both branch point compound not being discovered tryptophan and tyrosine was isolated from a earlier. Metzenberg and Mitchell (115) examined tryptophan auxotroph which accumulated an- a mutant of Neurospora crassa, which probably thranilate. The double mutant was then treated accumulated chorismate, in an attempt to find a to obtain the triple mutant (Aerobacter aerogenes branch point compound, but they found pre- 62-1), in which tryptophan and tyrosine were phenate among other compounds. essential for growth, whereas phenylalanine Chorismate has also been isolated from culture stimulated growth. Cell-free extracts were pre- fluids of E. coli (107), N. crassa (41), and Sac- pared from this strain grown with excess trypto- charomyces cerevisiae (107), and it is also metabo- phan to repress the enzyme system forming lized by cell extracts from Lactobacillus arabinosus anthranilate. These cell extracts formed a new (103), N. crassa (41), Claviceps paspalis (106), compound from a mixture of shikimate, ribose- yeast (50, 104), and plants (27), indicating the 5-phosphate, adenosine triphosphate (ATP), and general role of the compound in aromatic bio- Mge+. This compound could be converted to synthesis. anthranilate in the presence of glutamine by cell extracts of a multiple aromatic auxotroph with 1.0911 a metabolic block immediately after 3-enol- r 4-Aminobenzoate pyruvylshikimate 5-phosphate. The new com- pound was readily isolated on paper chromato- grams and could be shown to be enzymically 0.9 converted not only to anthranilate but also to prephenate (and thence to phenylpyruvate and 4-hydroxyphenylpyruvate), 4-hydroxybenzoate 0.- FIP (at that time,