Identification of the phosphocarrier protein enzyme IIIgut: essential component of the glucitol phosphotransferase system in Salmonella typhimurium.

The phosphoenolpyruvate-dependent phosphorylation of glucitol has been shown to require four distinct proteins in Salmonella typhimurium: two general energy-coupling proteins, enzyme I and HPr, and two glucitol-specific proteins, enzyme IIgut and enzyme IIIgut. The enzyme IIgut was solubilized from the membrane and purified about 100-fold, free of the other protein constituents of the phosphotransferase system. Enzyme IIIgut was found in both the soluble and the membrane fractions. The soluble enzyme IIIgut was purified to near homogeneity by gel filtration, hydroxylapatite chromatography, and hydrophobic chromatography on butylagarose. It was sensitive to parital inactivation by trypsin and N-ethylmaleimide, but was stable at 80 degrees C. The protein had an approximate molecular weight of 15,000. It was phosphorylated in the presence of phosphoenolpyruvate, enzyme I, and HPr, and this phosphoprotein was dephosphorylated in the presence of enzyme IIgut and glucitol. Antibodies were raised against enzyme IIIgut. Enzyme IIIglc and enzyme IIIgut exhibited no enzymatic or immunological cross-reactivity. Enzyme IIgut, enzyme IIIgut, and glucitol phosphate dehydrogenase activities were specifically induced by growth in the presence of glucitol. These results serve to characterize the glucitol-specific proteins of the phosphotransferase system in S. typhimurium.