Purification and characterization of the IIIXtl phospho-carrier protein of the phosphoenolpyruvate-dependent xylitol:phosphotransferase found in Lactobacillus casei C183.

The phosphoenolpyruvate-dependent xylitol:phosphotransferase system of Lactobacillus casei strain C183 requires a small, soluble, substrate-specific protein for catalytic activity. Designated enzyme IIIXtl (or IIIXtl), the protein was purified to electrophoretic homogeneity and characterized. IIIXtl, as purified, is a single polypeptide composed of 109 amino acid residues. It has an estimated molecular weight of 12,000 and is hydrophobic in nature. The hydrophobicity of IIIXtl is apparently due to the fact that the enzyme was isolated as the phosphorylated phosphocarrier protein. Removal of the phosphate group with alkaline phosphatase results in the loss of immunological cross-reactivity with anti-P-IIIXtl and an alteration in charge. The L. casei C183 IIIXtl is antigenically related to enzymes IIIXtl in Streptococcus avium and other, genetically distinct strains of L. casei.