Slee A M, Tanzer J M
Biochim Biophys Acta. 1982 Nov 22;692(3):415-24. doi: 10.1016/0005-2736(82)90392-3.
The transport of sucrose by selected mutant and wild-type cells of Streptococcus mutans was studied using washed cocci harvested at appropriate phases of growth, incubated in the presence of fluoride and appropriately labelled substrates. The rapid sucrose uptake observed cannot be ascribed to possible extracellular formation of hexoses from sucrose and their subsequent transport, formation of intracellular glycogen-like polysaccharide, or binding of sucrose or extracellular glucans to the cocci. Rather, there are at least three discrete transport systems for sucrose, two of which are phosphoenolpyruvate-dependent phosphotransferases with relatively low apparent Km values and the other a non-phosphotransferase (non-PTS) third transport system (termed TTS) with a relatively high apparent Km. For strain 6715-13 mutant 33, the Km values are 6.25 X 10(-5) M, 2.4 X 10(-4) M, and 3.0 X 10(-3) M, respectively: strain NCTC-10449, the Km values are 7.1 X 10(-5) M, 2.5 X 10(-4) M and 3.3 X 10(-3) M, respectively. The two lower Km systems could not be demonstrated in mid-log phase glucose-adapted cocci, a condition known to repress sucrose-specific phosphotransferase activity, but under these conditions the highest Km system persists. Also, a mutant devoid of sucrose-specific phosphotransferase activity fails to evidence the two high affinity (low apparent Km) systems, but still has the lowest affinity (highest Km) system. There was essentially no uptake at 4 degrees C indicating these processes are energy dependent. The third transport system, whose nature is unknown, appears to function under conditions of sucrose abundance and rapid growth which are known to repress phosphoenolpyruvate-dependent sucrose-specific phosphotransferase activity in S. mutans. These multiple transport systems seem well-adapted to S. mutans which is faced with fluctuating supplies of sucrose in its natural habitat on the surfaces of teeth.
利用在生长的适当阶段收获的洗涤过的球菌，在氟化物和适当标记的底物存在下进行培养，研究了变形链球菌的选定突变体和野生型细胞对蔗糖的转运。观察到的快速蔗糖摄取不能归因于蔗糖可能在细胞外形成己糖及其随后的转运、细胞内糖原样多糖的形成，或蔗糖或细胞外葡聚糖与球菌的结合。相反，蔗糖至少有三种不同的转运系统，其中两种是磷酸烯醇丙酮酸依赖性磷酸转移酶，其表观Km值相对较低，另一种是具有相对较高表观Km的非磷酸转移酶（非PTS）第三转运系统（称为TTS）。对于菌株6715 - 13突变体33，Km值分别为6.25×10⁻⁵M、2.4×10⁻⁴M和3.0×10⁻³M；对于菌株NCTC - 10449，Km值分别为7.1×10⁻⁵M、2.5×10⁻⁴M和3.3×10⁻³M。在对数中期适应葡萄糖的球菌中无法证明两个较低Km的系统，已知这种条件会抑制蔗糖特异性磷酸转移酶活性，但在这些条件下，最高Km的系统仍然存在。此外，缺乏蔗糖特异性磷酸转移酶活性的突变体无法证明两个高亲和力（低表观Km）系统，但仍然具有最低亲和力（最高Km）系统。在4℃时基本上没有摄取，表明这些过程是能量依赖性的。第三种转运系统的性质未知，似乎在蔗糖丰富和快速生长的条件下起作用，已知这些条件会抑制变形链球菌中磷酸烯醇丙酮酸依赖性蔗糖特异性磷酸转移酶的活性。这些多种转运系统似乎很好地适应了变形链球菌，该菌在牙齿表面的自然栖息地中面临着蔗糖供应的波动。
