3-Deoxy-d-arabino-Heptulosonate 7-Phosphate Synthase from Carrot Root (Daucus carota) Is a Hysteretic Enzyme

Roots of carrots (Daucus carota) contain three activities of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase, the enzyme that catalyzes the first step of the shikimate pathway. The three activities, enzymes I, II, and III, are separated by chromatography on phosphocellulose. Enzyme III,...

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Bibliographic Details
Published in:Plant physiology (Bethesda) 1985-11, Vol.79 (3), p.765-770
Main Authors: Suzich, JoAnn A., Jeffrey F. D. Dean, Herrmann, Klaus M.
Format: Article
Language:English
Subjects:
Allosteric regulation
Analytical, structural and metabolic biochemistry
Antibodies
Biological and medical sciences
Biosynthesis
Cyclic amino acids
Enzyme activity
Enzymes
Enzymes and enzyme inhibitors
Fundamental and applied biological sciences. Psychology
Gels
Lyases
Plant roots
Plants
Shikimate pathway
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Summary:Roots of carrots (Daucus carota) contain three activities of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase, the enzyme that catalyzes the first step of the shikimate pathway. The three activities, enzymes I, II, and III, are separated by chromatography on phosphocellulose. Enzyme III, purified to electrophoretic homogeneity, has a native molecular weight of 103,000 and consists of two identical subunits of 53,000 daltons each. Double reciprocal plots of reaction velocity versus substrate concentration yield Km values of 0.03 and 0.07 millimolar for P-enolpyruvate and erythrose-4-P, respectively. Both products, DAHP and orthophosphate, inhibit the enzyme. Enzyme III is a hysteretic enzyme that is activated by physiological concentrations of L-tryptophan and Mn2+, both of which also partially eliminate the hysteretic lag. Feedback activation of carrot DAHP synthase by tryptophan is interpreted to be an early regulatory signal for polyphenol biosynthesis. The three carrot DAHP synthase isoenzymes share antigenic determinants.
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.79.3.765