An alteration in phosphofructokinase 2 of Escherichia coli which impairs gluconeogenic growth and improves growth on sugars.
An alteration in phosphofructokinase 2 of Escherichia coli which impairs gluconeogenic growth and improves growth on sugars.
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大肠杆菌磷酸果糖激酶 2 的改变会损害糖异生生长并促进糖的生长。
DOI：
10.1111/j.1432-1033.1982.tb06790.x
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
Fraenkel,DG
中科院分区：
文献类型：
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作者：
Daldal,F;Babul,J;Guixé,V;Fraenkel,DG
大肠杆菌含有一种主要的磷酸果糖激酶同工酶，磷酸果糖激酶1，它是变构的，和一种次要的同工酶，磷酸果糖激酶2。已知pfkB 1突变增加磷酸果糖激酶2的量并允许缺乏磷酸果糖激酶1的突变体在糖上生长;它不影响在诸如甘油或乳酸盐的物质上的生长（即，“非同源生长”）。然而，在具有不同等位基因pfkBl* 的菌株中，致炎性生长显著受损。我们在这里显示，pfkBl * 的菌株含有一种改变形式的磷酸果糖激酶2，称为磷酸果糖激酶2*，已被纯化。磷酸果糖激酶2* 是冷不稳定的，其动力学特性与磷酸果糖激酶2略有不同，包括对1，6-二磷酸果糖的抑制作用不太敏感。磷酸果糖激酶2和磷酸果糖激酶2* 中6-磷酸果糖的Km值都很低（约5 × 10− 5 M）。然而，在缺乏磷酸果糖激酶1的菌株中，高水平的磷酸果糖激酶2与葡萄糖生长期间异常高浓度的单磷酸己糖相关，而具有磷酸果糖激酶2* 而不是磷酸果糖激酶2的菌株在葡萄糖上生长更快，并且含有较低水平的单磷酸己糖。相比之下，在致突变条件下，磷酸果糖激酶2菌株中的一磷酸己糖水平是正常的，而磷酸果糖激酶2* 菌株的生长受损与高水平的果糖2，6-二磷酸和非常低水平的一磷酸己糖有关。这些结果表明，磷酸果糖激酶2，如体外研究的那样，不应再被视为“非变构”蛋白，Kotlarz和布克根据不同类型的实验也得出了一个结论[Eur. 117，569-574（1981）]。磷酸果糖激酶2的突变改变允许在葡萄糖上更快速的生长但严重损害促细胞生长的事实表明了体内调节的重要性。突变体在葡萄糖上更快速的生长可能是基于对抑制剂（可能但不一定是果糖1，6-二磷酸）的敏感性降低来解释的，尽管其他模型也是可能的。关于致炎性损伤的机制，人们提出了各种各样的推测。
Escherichia colicontains a major phosphofructokinase isoenzyme, phosphofructokinase 1, which is allosteric, and a minor isoenzyme, phosphofructokinase 2. ThepfkBlmutation is known to increase the amount of phosphofructokinase 2 and allow growth on sugars of mutants lacking phosphofructokinase 1; it does not affect growth on substances such as glycerol or lactate (i.e., ‘gluconeogenic growth’). However, gluconeogenic growth is markedly impaired in strains with a different allele,pfkBl*. We show here that strains withpfkBl* contain an altered form of phosphofructokinase 2, called phosphofructokinase 2*, which has been purified. Phosphofructokinase 2* is cold labile and has slightly different kinetic characteristics from phosphofructokinase 2, which include being less sensitive to inhibition by fructose 1,6‐bisphosphate.TheKmfor fructose 6‐phosphate is low (about 5 × 10−5M) in both phosphofructokinase 2 and phosphofructokinase 2*. However, in strains lacking phosphofructokinase 1, a high level of phosphofructokinase 2 is associated with unusually high concentrations of hexose monophosphates during growth on glucose, while a strain with phosphofructokinase 2* instead of phosphofructokinase 2 grows more rapidly on glucose and contains lower levels of hexose monophosphates. In gluconeogenic conditions, by contrast, hexose monophosphate levels are normal in phosphofructokinase 2 strains, while the impaired growth of phosphofructokinase 2* strains is associated with high levels of fructose 2,6‐bisphosphate and very low levels of hexose monophosphates.These results show that phosphofructokinase 2, as studiedin vitro, should no longer be regarded as a ‘non‐allosteric’ protein, a conclusion also reached by Kotlarz and Buc on the basis of different types of experiments [Eur. J. Biochem. 117, 569–574 (1981)]. The fact that mutational alteration of phosphofructokinase 2 allows more rapid growth on glucose but severely impairs gluconeogenic growth is an indication of the significance of the regulationin vivo.The more rapid growth of the mutant on glucose might be explained on the basis of decreased sensitivity to an inhibitor (possibly, but not necessarily, fructose 1,6‐bisphosphate), although other models are possible. A variety of speculations are offered as to the mechanism of gluconeogenic impairment.