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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Facilitated diffusion of fructose via the phosphoenolpyruvate/glucose phosphotransferase system of Escherichia coli
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Facilitated diffusion of fructose via the phosphoenolpyruvate/glucose phosphotransferase system of Escherichia coli

机译：通过大肠杆菌的磷酸烯醇丙酮酸/葡萄糖磷酸转移酶系统促进果糖的扩散

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摘要

From mutants of Escherhoia coli unable to utilize fructose via the phosphoenolpyruvate/glycose phosphotransferase system (PTS). further mutants were selected that grow on fructose as the sole carbon source. albeit with relatively low affinity for that hexose (Km for growth rs8 mM but with Vm.. for generation time ca1 h 10 min): the fructose thus taken into the cells is phosphorylated to fructose 6-phosphate by ATP and a tytosolic frutto(manno)kinase (Mak). The gene effecting the translocation of fructose was iden- tified by Hfr-mediated conjugations and by phage-mediated trans- duction as specifying an isoform of the membrane-spanning en- zyme lIGIc of the PTS, which we designate ptSG-F Exconjugants that had acquired ptsG+ from Hfr strains used for mapping (designated ptsG-0 grew very poorly on fructose (Vm.. ss7 h 20 min), even though they were rich in Mak activity. A mutant of E coIi aIso rich in Mak but unable to grow on glucose by virtue of transposon- mediated inactivations both of ptSG and of the genes specifying enzyme lIMan (manXYD was restored to growth on glucose by plasmids containing either ptSG-F or ptSG-I, but only the former restored growth on fructose. Sequence anaIysis showed that the difference between these two forms of ptsG which was reflected also by differences in the rates at which they translocated mannose and glucose analogs such as methyl alpha-glucoside and 2-deoxyglu- cose, resided in a substitution of G in ptSG-I by T in ptSG-F in the first position of codon 12, with consequent replacement of valine by phenylalanine in the deduced amino acid sequence.
机译：来自不能通过磷酸烯醇丙酮酸/葡萄糖磷酸转移酶系统（PTS）利用果糖的大肠杆菌突变体。选择了在果糖上生长作为唯一碳源的其他突变体。尽管对己糖的亲和力相对较低（Km增长rs8 mM，但Vm ..生成时间约1小时10分钟）：如此进入细胞的果糖被ATP和苯酚型果糖磷酸化为6磷酸果糖（甘露糖）激酶（Mak）。 Hfr介导的缀合和噬菌体介导的转导确定了影响果糖易位的基因，指定了PTS的跨膜酶lIGIc的同工型，我们将ptSG-F缀合物指定为从Hfr菌株获得的ptsG +用于作图（指定的ptsG-0在果糖上（Vm .. ss7 h 20分钟）生长非常差，即使它们富含Mak活性。通过转座子介导的ptSG和指定liman酶基因的失活来抑制葡萄糖（manXYD通过含有ptSG-F或ptSG-1的质粒在葡萄糖上恢复生长，但只有前者在果糖上恢复生长。结果表明，这两种形式的ptsG之间的差异也反映在它们转移甘露糖和葡萄糖类似物（例如甲基α-葡萄糖苷和2-脱氧葡萄糖）的速率差异上，这些差异在于pt中G的取代SG-1在ptSG-F中位于T密码子12的第一个位置，随后在推导的氨基酸序列中被苯丙氨酸取代缬氨酸。

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