End product control of tryptophan biosynthesis in extracts and intact cells of the higher plant nicotina tabacum var. Wisconsin 38

Belser, William L.; Murphy, Joseph B.; Delmar, D.P.; Mills, Stanley E.

doi:10.1016/0304-4165(71)90023-7

Cited by 57 publications

(21 citation statements)

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“…plants (4,19). In contrast to microbial systems, however, evidence of end-product control of the concentration of a number of key biosynthetic enzymes has not been obtained in higher plants (2,7,13,20,22,30). This may reflect significant differences in the range and extent of regulatory mechanisms which serve to balance metabolism in dissimilar organisms.…”

Section: Introductionmentioning

confidence: 83%

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Changes in Enzyme Regulation during Growth of Maize

Matthews

Gurman²,

Bryan³

1975

Plant Physiol.

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The sensitivity of homoserine dehydrogenase (EC 1.1.1.3) to inhibition by the feed-back modifier, L-threonine, was examined in preparations derived from etiolated shoots, roots, and lightgrown tissues of Zea mays L. var. earliking. A progressive decrease in enzyme sensitivity was observed during seedling growth. Enzyme derived from internode tissue retained a greater sensitivity to the effector than enzyme derived from apical portions of etiolated shoots, whereas enzyme from root tips was characteristically more sensitive than that prepared from mature cells of the root. Enzyme desensitization occurred rapidly during culture of excised shoots and the activities of both homoserine dehydrogenase and aspartokinase (EC 2.7.2.4) declined during shoot culture under a variety of conditions. The initial enzyme levels and the characteristic sensitivity of homoserine dehydrogenase were preserved during culture at 5 to 7 C, but desensitization was not prevented by inclusion of cycloheximide in the culture medium.Results of control experiments provide evidence that desensitization occurs in vivo. No alteration of the enzyme properties was detected during extraction or concentration of sensitive or insensitive enzyme or during coextraction of enzyme from mixed populations of different age shoots; nor was a differential distribution of inhibitors or activators indicated during assay of mixed preparations. The change in enzyme sensitivity was apparent under a variety of assay conditions and was not accompanied by changes in the apparent affinity of the enzyme for the substrate, homoserine. It is suggested that systematic changes in the regulatory characteristics of certain enzymes could be an important level of metabolic regulation during cellular differentiation.Three forms of maize homoserine dehydrogenaase were detected after acrylamide gel electrophoresis of samples derived from 72-hr shoots. Similar analysis of samples from older shoots revealed a broad asymmetric band of enzyme activity, suggesting that changes in the relative distribution of specific forms of the enzyme could be related to the growth-dependent changes in the sensitivity of maize homoserine dehydrogenase. plants (4,19). In contrast to microbial systems, however, evidence of end-product control of the concentration of a number of key biosynthetic enzymes has not been obtained in higher plants (2,7,13,20,22,30). This may reflect significant differences in the range and extent of regulatory mechanisms which serve to balance metabolism in dissimilar organisms. A greater extent of metabolite compartmentation in structurally complex multicellular plants would be expected (24, 31), but unique mechanisms may also contribute to metabolic regulation in these organisms.The present experiments are concerned with alterations in the activities of homoserine dehydrogenase (EC 1 . 1 .1 . 3) and aspartokinase (EC 2.7.2.4) during development of Zea inays L. var. earliking. These enzymes contribute to the regulation of the biosynthetic pathway leading from aspartic...

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Section: Introductionmentioning

confidence: 83%

“…2 Present address: Department of Microbiology, The University of Rochester, School of Medicine and Dentistry, Rochester, N.Y. 14642.…”

mentioning

confidence: 99%

Changes in Enzyme Regulation during Growth of Maize

Matthews

Gurman²,

Bryan³

1975

Plant Physiol.

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“…Isoforms of the committing enzyme, chorismate mutase, are allosterically inhibited by phenylalanine and tyrosine, and stimulated by tryptophan (Eberhard et al, 1996;Coruzzi and Last, 2000). Anthranilate synthase, the committing enzyme for tryptophan biosynthesis, is inhibited by tryptophan (Belser et al, 1971). Similarly, arogenate dehydrogenase is feedback-inhibited by tyrosine (Rippert and Matringe, 2002).…”

Section: Introductionmentioning

confidence: 99%

Pleiotropic physiological consequences of feedback-insensitive phenylalanine biosynthesis in Arabidopsis thaliana

et al. 2010

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SUMMARYA large proportion of plant carbon flow passes through the shikimate pathway to phenylalanine, which serves as a precursor for numerous secondary metabolites. To identify new regulatory mechanisms affecting phenylalanine metabolism, we isolated Arabidopsis thaliana mutants that are resistant to the phytotoxic amino acid m-tyrosine, a structural analog of phenylalanine. Map-based cloning identified adt2-1D, a dominant point mutation causing a predicted serine to alanine change in the regulatory domain of ADT2 (arogenate dehydratase 2). Relaxed feedback inhibition and increased expression of the mutant enzyme caused up to 160-fold higher accumulation of free phenylalanine in rosette leaves, as well as altered accumulation of several other primary and secondary metabolites. In particular, abundance of 2-phenylethylglucosinolate, which is normally almost undetectable in leaves of the A. thaliana Columbia-0 accession, is increased more than 30-fold. Other observed phenotypes of the adt2-1D mutant include abnormal leaf development, resistance to 5-methyltryptophan, reduced growth of the generalist lepidopteran herbivore Trichoplusia ni (cabbage looper) and increased salt tolerance.

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“…For the synthesis of one molecule of Trp from chorismate, a single molecule of Gln and serine (Ser) is consumed. The final product Trp inhibits AS to regulate its production (Belser et al 1971;Widholm 1972). The Trp serves not only as a component of proteins, but also as a precursor of various secondary metabolites in plants (Fig.…”

Section: Trp Biosynthesis Regulation and Trp Related Secondary Metamentioning

confidence: 99%

Metabolomics for metabolically manipulated plants: effects of tryptophan overproduction

et al. 2007

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Advances in molecular breeding technologies have enabled manipulation of the concentrations of specific plant components by modifying the genes that play a key role in their production. This has provided new opportunities to enhance the nutritional quality of major crops. However, given that metabolic pathways form a highly integrated network, any alteration in a given biosynthetic pathway is most likely to effect secondary and unpredicted changes in the metabolite profile of other pathways. Metabolomics technologies can contribute to the efficient detection of such unexpected effects caused by genetic modification. This has relevance not only from the perspective of safety evaluations of newly developed crops, but to basic science focused on uncovering hitherto unknown regulatory mechanisms associated with the biosynthesis and catabolism of primary and secondary metabolites in plants. In this review, recent advances in plant metabolic engineering for the overproduction of tryptophan (Trp), one of the essential amino acids, are described. In particular, the efficacy of a transgene OASA1D that encodes a mutant anthranilate synthase (AS) a subunit of rice in specifically elevating levels of Trp without marked secondary effects on the metabolite profile of rice is demonstrated. Related topics, such as regulation of Trp biosynthesis, possible interactions between the biosyntheses of Trp and other aromatic amino acids, and translocation of Trp in are discussed based on findings derived from metabolomic analyses of Trp-overproducing transgenic plants.

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End product control of tryptophan biosynthesis in extracts and intact cells of the higher plant nicotina tabacum var. Wisconsin 38

Cited by 57 publications

References 14 publications

Changes in Enzyme Regulation during Growth of Maize

Changes in Enzyme Regulation during Growth of Maize

Pleiotropic physiological consequences of feedback-insensitive phenylalanine biosynthesis in Arabidopsis thaliana

Metabolomics for metabolically manipulated plants: effects of tryptophan overproduction

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