Chassy B M, Thompson J
J Bacteriol. 1983 Jun;154(3):1204-14. doi: 10.1128/jb.154.3.1204-1214.1983.
Cells of Lactobacillus casei grown in media containing galactose or a metabolizable beta-galactoside (lactose, lactulose, or arabinosyl-beta-D-galactoside) were induced for a galactose-phosphoenolpyruvate-dependent phosphotransferase system (gal-PTS). This high-affinity system (Km for galactose, 11 microM) was inducible in eight strains examined, which were representative of all five subspecies of L. casei. The gal-PTS was also induced in strains defective in glucose- and lactose-phosphoenolpyruvate-dependent phosphotransferase systems during growth on galactose. Galactose 6-phosphate appeared to be the intracellular inducer of the gal-PTS. The gal-PTS was quite specific for D-galactose, and neither glucose, lactose, nor a variety of structural analogs of galactose caused significant inhibition of phosphotransferase system-mediated galactose transport in intact cells. The phosphoenolpyruvate-dependent phosphorylation of galactose in vitro required specific membrane and cytoplasmic components (including enzyme IIIgal), which were induced only by growth of the cells on galactose or beta-galactosides. Extracts prepared from such cells also contained an ATP-dependent galactokinase which converted galactose to galactose 1-phosphate. Our results demonstrate the separate identities of the gal-PTS and the lactose-phosphoenol-pyruvate-dependent phosphotransferase system in L. casei.
在含有半乳糖或可代谢的β-半乳糖苷（乳糖、乳果糖或阿拉伯糖基-β-D-半乳糖苷）的培养基中生长的干酪乳杆菌细胞，会被诱导产生一种依赖磷酸烯醇丙酮酸的半乳糖磷酸转移酶系统（gal-PTS）。这种高亲和力系统（半乳糖的Km值为11 microM）在所检测的8个菌株中均可被诱导，这些菌株代表了干酪乳杆菌所有5个亚种。在以半乳糖为碳源生长时，葡萄糖和乳糖依赖磷酸烯醇丙酮酸的磷酸转移酶系统缺陷型菌株中，gal-PTS也会被诱导。6-磷酸半乳糖似乎是gal-PTS的细胞内诱导物。gal-PTS对D-半乳糖具有高度特异性，葡萄糖、乳糖或各种半乳糖结构类似物均不会对完整细胞中磷酸转移酶系统介导的半乳糖转运产生显著抑制。体外依赖磷酸烯醇丙酮酸的半乳糖磷酸化需要特定的膜和细胞质成分（包括酶IIIgal），这些成分仅在细胞以半乳糖或β-半乳糖苷为碳源生长时被诱导产生。从这些细胞制备的提取物中还含有一种依赖ATP的半乳糖激酶，可将半乳糖转化为1-磷酸半乳糖。我们的结果证明了干酪乳杆菌中gal-PTS和乳糖依赖磷酸烯醇丙酮酸的磷酸转移酶系统是各自独立存在的。
