PMID:3121621
| Citation |
Huynh, QK, Kishore, GM and Bild, GS (1988) 5-Enolpyruvyl shikimate 3-phosphate synthase from Escherichia coli. Identification of Lys-22 as a potential active site residue. J. Biol. Chem. 263:735-9 |
|---|---|
| Abstract |
5-Enolpyruvyl shikimate 3-phosphate synthase catalyzes the reversible condensation of phosphoenolpyruvate and shikimate 3-phosphate to yield 5-enolpyruvyl shikimate 3-phosphate and inorganic phosphate. The enzyme is a target for the nonselective herbicide glyphosate (N-phosphonomethylglycine). In order to determine the role of lysine residues in the mechanism of action of this enzyme as well as in its inhibition by glyphosate, chemical modification studies with pyridoxal 5'-phosphate were undertaken. Incubation of the enzyme with the reagent in the absence of light resulted in a time-dependent loss of enzyme activity. The inactivation followed pseudo first-order and saturation kinetics with Kinact of 45 microM and a maximum rate constant of 1.1 min-1. The inactivation rate increased with increase in pH, with a titratable pK of 7.6. Activity of the inactive enzyme was restored by addition of amino thiol compounds. Reaction of enzyme with pyridoxal 5'-phosphate was prevented in the presence of substrates or substrate plus glyphosate, an inhibitor of the enzyme. Upon 90% inactivation, approximately 1 mol of pyridoxal 5'-phosphate was incorporated per mol of enzyme. The azomethine linkage between pyridoxal 5'-phosphate and the enzyme was reduced by NaB3H4. Tryptic digestion followed by reverse phase chromatographic separation resulted in the isolation of a peptide which contained the pyridoxal 5'-phosphate moiety as well as 3H label. By amino acid sequencing of this peptide, the modified residue was identified as Lys-22. The amino acid sequence around Lys-22 is conserved in bacterial, fungal, as well as plant enzymes suggesting that this region may constitute a part of the enzyme's active site. |
| Links | |
| Keywords |
3-Phosphoshikimate 1-Carboxyvinyltransferase; Alkyl and Aryl Transferases; Amino Acid Sequence; Binding Sites; Chromatography, High Pressure Liquid; Escherichia coli/enzymology; Kinetics; Lysine; Peptide Fragments/analysis; Phosphoenolpyruvate/pharmacology; Shikimic Acid/analogs & derivatives; Shikimic Acid/metabolism; Transferases/antagonists & inhibitors; Transferases/metabolism; Trypsin/metabolism |
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