title: Evidence for covalently cross-linked dimers and trimers of enzyme I of the Escherichia coli phosphotransferase system.
abstract: Enzyme I of the bacterial phosphotransferase system catalyzes transfer of the phosphoryl moiety from phosphoenolpyruvate to both of the heat-stable phosphoryl carrier proteins of the phosphotransferase system, HPr and FPr. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-pressure liquid chromatography, we demonstrated the existence of covalently cross-linked enzyme I dimers and trimers. Enzyme I exchange assays and phosphorylation experiments with [32P]phosphoenolpyruvate showed that covalent dimers and trimers are catalytically active. Inhibitors of the enzyme I-catalyzed phosphoenolpyruvate-pyruvate exchange block the phosphorylation of enzyme I dimers and trimers. Inhibition of the activity of enzyme I by N-ethylmaleimide, but not that by p-chloromercuriphenylsulfonate, could be overcome by high concentrations of enzyme, suggesting that N-ethylmaleimide modification changes the associative properties of enzyme I. We present evidence for two distinct classes of sulfhydryl groups in enzyme I.
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D046911:Macromolecular Substances; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000037:antagonists & inhibitors; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D013439:Sulfhydryl Reagents; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System