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首页> 外文期刊>Journal of bacteriology >Mechanisms of Lactose Utilization by Lactic Acid Streptococci: Enzymatic and Genetic Analyses
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Mechanisms of Lactose Utilization by Lactic Acid Streptococci: Enzymatic and Genetic Analyses

机译：乳酸链球菌利用乳糖的机制：酶和遗传分析

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The apparent instability of β-galactosidase in toluene-treated cells or cell-free extracts of lactic streptococci is explained by the fact that these organisms do not contain the expected enzyme. Instead, various strains of Streptococcus lactis, S. cremoris, and S. diacetilactis were shown to hydrolyze o-nitrophenyl-β-d-galactoside-6-phosphate (ONPG-6-P), indicating the presence of a different enzyme. In addition, lactose metabolism in S. lactis C2F was found to involve enzyme I (EI), enzyme II (EII), factor III (FIII), and a heat-stable protein (HPr) of a phosphoenolpyruvate (PEP)-dependent phosphotransferase system analogous to that of Staphylococcus aureus. Mutants of S. lactis C2F, defective in lactose metabolism, possessed the phenotype lac? gal?. These strains were unable to accumulate 14C-thiomethyl-β-d-galactoside, to hydrolyze ONPG, or to utilize lactose when grown in lactose or galactose broth. In addition, these mutants contained EI and HPr, but lacked EII, FIII, and the ability to hydrolyze ONPG-6-P. This suggested that the defect was in the phosphorylation step. Lactose-negative mutants of S. lactis 7962, a strain containing β-galactosidase, could be separated into several classes, which indicated that this organism is not dependent upon the PEP-phosphotransferase system for lactose metabolism.
机译：β-半乳糖苷酶在经甲苯处理的细胞或乳酸链球菌的无细胞提取物中明显不稳定，这是因为这些生物体不含预期的酶。取而代之的是各种乳链球菌，乳链球菌和乳杆菌。研究表明双乙内酯水解 o -硝基苯基-β-d-半乳糖苷6-磷酸酯（ONPG-6-P），表明存在另一种酶。此外， S中的乳糖代谢。发现乳酸菌C 2 F涉及磷酸烯醇式丙酮酸的酶I（EI），酶II（EII），因子III（FIII）和热稳定蛋白（HPr）（ PEP）依赖性磷酸转移酶系统，类似于金黄色葡萄球菌。 S的突变体。乳糖代谢缺陷的乳酸 C 2 F具有表型lac ？ gal ？。这些菌株在乳糖或半乳糖肉汤中生长时，无法积聚 14 C-硫代甲基-β-d-半乳糖苷，无法水解ONPG或利用乳糖。此外，这些突变体包含EI和HPr，但缺少EII，FIII和水解ONPG-6-P的能力。这表明缺陷在磷酸化步骤中。 S的乳糖阴性突变体。含有β-半乳糖苷酶的乳酸菌7962可以分为几类，这表明该生物体不依赖于PEP-磷酸转移酶系统进行乳糖代谢。

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