Suppression of IIIGlc‐defects by Enzymes IINag and IIBgl of the PEP:carbohydrate phosphotransferase system

Summary The Enzymes II of the PEP:carbohydrate phosphotransferase system (PTS) specific for N‐acetylglucosamine (IINag) and β‐glucosides (IIBgl) contain C‐terminal domains that show homology with Enzyme IIIGlc of the PTS. We investigated whether one or both of the Enzymes II could substitute functionally for IIIGlc. The following results were obtained: (i) Enzyme IINag, synthesized from either a chromosomal or a plasmidencoded nagE+ gene could replace IIIGlc in glucose, methyl α‐glucoside and sucrose transport via the corresponding Enzymes II. An Enzyme IINag with a large deletion in the N‐terminal domain but with an intact C‐terminal domain could also replace IIIGlc in IIGlc‐dependent glucose transport, (ii) After decryptification of the Escherichia coli bgl operon, Enzyme IIBgl could substitute for IIIGlc. (iii) Phospho‐HPr‐dependent phosphorylation of methyl α‐glucoside via IINag/IIGlc is inhibited by antiserum against IIIGlc as is N‐acetyl‐glucosamine phosphorylation via IINag. (iv) In strains that contained the plasmid which coded for IINag, a protein band with a molecular weight of 62000 D could be detected with antiserum against IIIGlc. We conclude from these results that the IIIGlc‐like domain of Enzyme IINag and IIBgl can replace IIIGlc in IIIGlc‐dependent carbohydrate transport and phosphorylation.