Thompson J, Chassy B M, Egan W
J Bacteriol. 1985 Apr;162(1):217-23. doi: 10.1128/jb.162.1.217-223.1985.
A mutant of Streptococcus lactis 133 has been isolated that lacks both glucokinase and phosphoenolpyruvate-dependent mannose-phosphotransferase (mannose-PTS) activities. The double mutant S. lactis 133 mannose-PTSd GK- is unable to utilize either exogenously supplied or intracellularly generated glucose for growth. Fluorographic analyses of metabolites formed during the metabolism of [14C]lactose labeled specifically in the glucose or galactosyl moiety established that the cells were unable to phosphorylate intracellular glucose. However, cells of S. lactis 133 mannose-PTSd GK- readily metabolized intracellular glucose 6-phosphate, and the growth rates and cell yield of the mutant and parental strains on sucrose were the same. During growth on lactose, S. lactis 133 mannose-PTSd GK- fermented only the galactose moiety of the disaccharide, and 1 mol of glucose was generated per mol of lactose consumed. For an equivalent concentration of lactose, the cell yield of the mutant was 50% that of the wild type. The specific rate of lactose utilization by growing cells of S. lactis 133 mannose-PTSd GK- was ca. 50% greater than that of the wild type, but the cell doubling times were 70 and 47 min, respectively. High-resolution 31P nuclear magnetic resonance studies of lactose transport by starved cells of S. lactis 133 and S. lactis 133 mannose-PTSd GK- showed that the latter cells contained elevated lactose-PTS activity. Throughout exponential growth on lactose, the mutant maintained an intracellular steady-state glucose concentration of 100 mM. We conclude from our data that phosphorylation of glucose by S. lactis 133 can be mediated by only two mechanisms: (i) via ATP-dependent glucokinase, and (ii) by the phosphoenolpyruvate-dependent mannose-PTS system.
已分离出乳酸链球菌133的一个突变体，该突变体缺乏葡萄糖激酶和磷酸烯醇丙酮酸依赖性甘露糖磷酸转移酶（甘露糖-PTS）活性。双突变体乳酸链球菌133甘露糖-PTSd GK-无法利用外源供应的或细胞内产生的葡萄糖进行生长。对[14C]乳糖代谢过程中形成的代谢物进行荧光分析，这些乳糖在葡萄糖或半乳糖部分进行了特异性标记，结果表明细胞无法将细胞内的葡萄糖磷酸化。然而，乳酸链球菌133甘露糖-PTSd GK-的细胞能够轻易地代谢细胞内的葡萄糖6-磷酸，并且该突变体菌株和亲本菌株在蔗糖上的生长速率和细胞产量相同。在乳糖上生长期间，乳酸链球菌133甘露糖-PTSd GK-仅发酵二糖的半乳糖部分，每消耗1摩尔乳糖会产生1摩尔葡萄糖。对于同等浓度的乳糖，突变体的细胞产量是野生型的50%。生长中的乳酸链球菌133甘露糖-PTSd GK-细胞利用乳糖的比速率比野生型大约高50%，但细胞倍增时间分别为70分钟和47分钟。对饥饿的乳酸链球菌133和乳酸链球菌133甘露糖-PTSd GK-细胞进行的乳糖转运的高分辨率31P核磁共振研究表明，后一种细胞含有升高的乳糖-PTS活性。在乳糖上的整个指数生长过程中，突变体维持细胞内葡萄糖的稳态浓度为100 mM。我们从数据中得出结论，乳酸链球菌133对葡萄糖的磷酸化仅可通过两种机制介导：（i）通过ATP依赖性葡萄糖激酶，以及（ii）通过磷酸烯醇丙酮酸依赖性甘露糖-PTS系统。
