title: 5-Enolpyruvyl shikimate 3-phosphate synthase from Escherichia coli. Identification of Lys-22 as a potential active site residue.
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.
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D019883:Alkyl and Aryl Transferases; D000595:Amino Acid Sequence; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008239:Lysine; D010446:Peptide Fragments / Q000032:analysis; D010728:Phosphoenolpyruvate / Q000494:pharmacology; D012765:Shikimic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D014166:Transferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D012765:Shikimic Acid; C042786:shikimic acid-3-phosphate; D010728:Phosphoenolpyruvate; D014166:Transferases; D019883:Alkyl and Aryl Transferases; D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D014357:Trypsin; D008239:Lysine