Mannitol-specific carrier protein from the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system can be extracted as a dimer from the membrane.
The association state of the mannitol-specific enzyme II (EIIMtl) has been studied both in the purified form and embedded in the cytoplasmic membrane. Membrane fragments obtained from mannitol-grown Escherichia coli catalyze the phosphoenolpyruvate- (PEP) dependent phosphorylation of both glucose and mannitol; thus they contain both the glucose- and mannitol-specific enzymes II. The autoradiogram of an electrophoresed mixture of [32P]PEP, EI, HPr, and membrane fragments shows bands at 58 and 116 kilodaltons, in addition to the bands of P-EI and P-HPr. In an analogous experiment with purified EIIMtl, suspended in detergent micelles, only a 58 000-dalton band and the P-HPr and P-EI bands were found. Treatment of the phosphorylated membranes with mannitol results in an immediate substantial decrease in the radioactivity in the 58- and 116-kilodalton bands. A similar treatment of the phosphorylated membranes with glucose had no direct effect on the autoradiogram. We conclude therefore that the 58- and 116-kilodalton bands originate from enzyme IIMtl monomers and dimers, respectively. The interaction between the subunits of the dimer is not abolished by the addition of up to 5% sodium dodecyl sulfate. However, the nonionic detergent Lubrol PX, which is present during the purification of EIIMtl, is capable of transforming the enzyme IIMtl dimers into monomers.
D002462:Cell Membrane / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008353:Mannitol / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D008970:Molecular Weight; D009004:Monosaccharide Transport Proteins; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D013379:Substrate Specificity
D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D008353:Mannitol; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C022358:mannitol PTS permease, E coli