A unique reaction in a common pathway: mechanism and function of chorismate synthase in the shikimate pathway |
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Authors: | Peter Macheroux Jürg Schmid Nikolaus Amrhein Andreas Schaller |
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Institution: | Swiss Federal Institute of Technology, Institute of Plant Sciences, Universit?tstr. 2, CH-8092 Zürich, Switzerland, CH
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Abstract: | Chorismate synthase, the seventh enzyme in the shikimate pathway, catalyzes the transformation of 5-enolpyruvylshikimate 3-phosphate
to chorismate which is the last common precursor in the biosynthesis of numerous aromatic compounds in bacteria, fungi and
plants. The enzyme has an absolute requirement for reduced FMN as a cofactor, although the 1,4-anti elimination of phosphate and the C(6proR)-hydrogen does not involve a net redox change. The role of the reduced FMN in catalysis has long been elusive. However, recent
detailed kinetic and bioorganic approaches have fundamentally advanced our understanding of the mechanism of action, suggesting
an initial electron transfer from tightly bound reduced flavin to the substrate, a process which results in C—O bond cleavage.
Studies on chorismate synthases from bacteria, fungi and plants revealed that in these organisms the reduced FMN cofactor
is made available in different ways to chorismate synthase: chorismate synthases in fungi – in contrast to those in bacteria
and plants – carry a second enzymatic activity which enables them to reduce FMN at the expense of NADPH. Yet, as shown by
the analysis of the corresponding genes, all chorismate synthases are derived from a common ancestor. However, several issues
revolving around the origin of reduced FMN, as well as the possible regulation of the enzyme activity by means of the availability
of reduced FMN, remain poorly understood. This review summarizes recent developments in the biochemical and genetic arena
and identifies future aims in this field.
Received: 22 June 1998 / Accepted: 7 August 1998 |
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Keywords: | : Aromatic amino acids Chorismate synthase Flavin reductase Shikimate pathway |
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