title: Unmasking of an essential thiol during function of the membrane-bound enzyme II of the phosphenolpyruvate beta-glucoside phosphotransferase system of Escherichia coli.
abstract: beta-Glucoside transport by phosphoenolpyruvate-hexose phosphotransferase system in Escherichia coli is inactivated in vivo by thiol reagents. This inactivation is strongly enhanced by the presence of transported substrates. In a system reconstituted from soluble and membrane-bound components, only the particulate component, the membrane-bound enzyme IIbgl appeared as the target of N-ethylmaleimide inaction. The same feature was found in the case of methyl-alpha-D-glucoside uptake via enzyme IIglc. It is shown that the sensitizing effect of substrates is specific and not generalized, methyl-alpha-D-glucoside only sensitizes enzyme IIglc and p-nitrophenyl-beta-D-glucoside only sensitizes enzyme IIbgl towards N-ethylmaleimide inactivation. The inactivation of enzyme IIbgl by thiol reagents is also promoted in vivo by fluoride inhibition of phosphoenolpyruvate synthesis. In toluene-treated bacteria, the presence of phosphoenolpyruvate protects against inactivation by thiol reagents of p-nitrophenyl-beta-D-glucoside phosphorylation. Both results suggest that the inactivator resistent form of enzyme IIbgl is an energized form of the enzyme.
mesh_terms: D002729:Chloromercuribenzoates / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology*; D005033:Ethylmaleimide / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology; D005960:Glucosides / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism*; D007700:Kinetics; D009097:Multienzyme Complexes / Q000378:metabolism*; D010728:Phosphoenolpyruvate; D010770:Phosphotransferases / Q000378:metabolism*; D013045:Species Specificity; D013438:Sulfhydryl Compounds
chemical_list: D002729:Chloromercuribenzoates; D005960:Glucosides; D006027:Glycosides; D009097:Multienzyme Complexes; D013438:Sulfhydryl Compounds; D010728:Phosphoenolpyruvate; D010770:Phosphotransferases; D005033:Ethylmaleimide; D005459:Fluorides