Shikimate
Páginas: 23 (5675 palabras)
Publicado: 14 de noviembre de 2012
Pergamon
0031-9422(94)00962-7
Phytochemistry, Vol. 39, No. 4, pp. 737-749, 1995
Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031 9422/95 $29.50 + 0.00
REVIEW ARTICLE NUMBER 104 MOLECULAR ORGANIZATION OF THE SHIKIMATE PATHWAY IN HIGHER PLANTS
JORO SCHMID and NIKOLAUSAMRHEIN Institute of Plant Sciences, Swiss Federal Institute of Technology,Universithtstrasse 2, CH-8092 Ziirich, Switzerland
(Received 14 November 1994)
Key Word Index--Biosynthesis of the aromatic amino adds; shikimate pathway; phenylalanine; tyrosine; tryptophan; genetic organization; higher plants.
Abstract--The shikimate pathway produces the three proteinogenic aromatic amino adds, phenylalanine, tyrosine and tryptophan, which are, in addition to severalintermediates of the shikimate pathway, intermediates in the biosynthesis of numerous aromatic natural products in higher plants. While there is only little difference in the sequence of the chemical reactions of the pathway in bacteria, fungi and plants, considerable differences exist in the organization and regulation of the shikimate pathway in plants, fungi and bacteria. The recent isolation andcharacterization of cDNAs and genes coding for enzymes of the shikimate pathway in higher plants have confirmed that plastids are the major, if not only site of aromatic amino acid biosynthesis in plants. Furthermore, the observed differential spatial and temporal expression of genes coding for isozymes of the pathway indicates a complex regulation that we are only beginning to understand.INTRODUCTION In nature, thousands of compounds are known which contain one or more aromatic rings. These compounds are predominantly synthesized via the shikimate pathway and its many branches, the most prominent and essential products being the three proteinogenic aromatic amino acids, i.e. phenylalanine, tyrosine and tryptophan. The occurrence of the pathway is restricted to plants, fungi and bacteria,therefore making aromatic amino acids essential in the diets of animals. As important as the aromatic amino acids are, they represent only a fraction of known products of the shikimate pathway and are themselves precursors to a myriad of other aromatic natural products (for recent reviews, see I-1-5]). Due to the diversity of aromatic metabolism in various classes of organisms, this review will beconfined to the plant kingdom. Our main aim is to provide a summary of recent data on aromatic amino acid biosynthesis in higher plants, focusing on results obtained by applying techniques of molecular biology.
Aromatic amino acids as structural units of proteins and precursors of secondary metabolites
In plants, proteins are synthesized in three different compartments: in the cytoplasm, inthe plastids, and in
the mitochondria. Therefore, the aromatic amino acids must either be synthesized in situ in the respective protein synthesizing compartment or they are synthesized outside this compartment and have to be imported. In the case of mitochondria, there is no evidence to suggest that the aromatic amino acids are synthesized in these organelles; therefore, one can envisagecarrier-mediated transport of the aromatic amino acids across the mitochondrial membranes. On the other hand, it is well established by the work of Schultz and associates, that all the three aromatic amino acids can be synthesized in plastids ['6, 7]. It is a matter of debate, however, whether there is, in addition, a complete pathway in the cytoplasm, or whether the aromatic amino acids are synthesizedexclusively in the plastids [5, 8-11]. All three aromatic amino acids, besides being structural units of proteins, serve as precursors of secondary plant products and, in this respect, represent pathway intermediates. Some of the shikimate pathway intermediates serve also as direct precursors of secondary plant products. Some of these are widely represented across the plant kingdom whereas others...
0031-9422(94)00962-7
Phytochemistry, Vol. 39, No. 4, pp. 737-749, 1995
Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031 9422/95 $29.50 + 0.00
REVIEW ARTICLE NUMBER 104 MOLECULAR ORGANIZATION OF THE SHIKIMATE PATHWAY IN HIGHER PLANTS
JORO SCHMID and NIKOLAUSAMRHEIN Institute of Plant Sciences, Swiss Federal Institute of Technology,Universithtstrasse 2, CH-8092 Ziirich, Switzerland
(Received 14 November 1994)
Key Word Index--Biosynthesis of the aromatic amino adds; shikimate pathway; phenylalanine; tyrosine; tryptophan; genetic organization; higher plants.
Abstract--The shikimate pathway produces the three proteinogenic aromatic amino adds, phenylalanine, tyrosine and tryptophan, which are, in addition to severalintermediates of the shikimate pathway, intermediates in the biosynthesis of numerous aromatic natural products in higher plants. While there is only little difference in the sequence of the chemical reactions of the pathway in bacteria, fungi and plants, considerable differences exist in the organization and regulation of the shikimate pathway in plants, fungi and bacteria. The recent isolation andcharacterization of cDNAs and genes coding for enzymes of the shikimate pathway in higher plants have confirmed that plastids are the major, if not only site of aromatic amino acid biosynthesis in plants. Furthermore, the observed differential spatial and temporal expression of genes coding for isozymes of the pathway indicates a complex regulation that we are only beginning to understand.INTRODUCTION In nature, thousands of compounds are known which contain one or more aromatic rings. These compounds are predominantly synthesized via the shikimate pathway and its many branches, the most prominent and essential products being the three proteinogenic aromatic amino acids, i.e. phenylalanine, tyrosine and tryptophan. The occurrence of the pathway is restricted to plants, fungi and bacteria,therefore making aromatic amino acids essential in the diets of animals. As important as the aromatic amino acids are, they represent only a fraction of known products of the shikimate pathway and are themselves precursors to a myriad of other aromatic natural products (for recent reviews, see I-1-5]). Due to the diversity of aromatic metabolism in various classes of organisms, this review will beconfined to the plant kingdom. Our main aim is to provide a summary of recent data on aromatic amino acid biosynthesis in higher plants, focusing on results obtained by applying techniques of molecular biology.
Aromatic amino acids as structural units of proteins and precursors of secondary metabolites
In plants, proteins are synthesized in three different compartments: in the cytoplasm, inthe plastids, and in
the mitochondria. Therefore, the aromatic amino acids must either be synthesized in situ in the respective protein synthesizing compartment or they are synthesized outside this compartment and have to be imported. In the case of mitochondria, there is no evidence to suggest that the aromatic amino acids are synthesized in these organelles; therefore, one can envisagecarrier-mediated transport of the aromatic amino acids across the mitochondrial membranes. On the other hand, it is well established by the work of Schultz and associates, that all the three aromatic amino acids can be synthesized in plastids ['6, 7]. It is a matter of debate, however, whether there is, in addition, a complete pathway in the cytoplasm, or whether the aromatic amino acids are synthesizedexclusively in the plastids [5, 8-11]. All three aromatic amino acids, besides being structural units of proteins, serve as precursors of secondary plant products and, in this respect, represent pathway intermediates. Some of the shikimate pathway intermediates serve also as direct precursors of secondary plant products. Some of these are widely represented across the plant kingdom whereas others...
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