Castro L, Feucht B U, Morse M L, Saier M H
J Biol Chem. 1976 Sep 25;251(18):5522-7.
Carbohydrate uptake and cyclic adenosine 3':5'-monophosphate (cyclic AMP) synthesis were studied employing mutant strains of Escherichia coli in which Enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system was heat-labile. Partial loss of Enzyme I activity, which resulted from incubation of cells at the nonpermissive temperature, depressed the rate and extent of methyl alpha-glucoside uptake. Temperature inactivation of Enzyme I also rendered cyclic AMP synthesis and the uptake of several carbohydrates (glycerol, maltose, melibiose, and lactose) hypersensitive to inhibition by methyl alpha-glucoside. Protein synthesis did not appear to be required for these effects. The parental strains and "revertant" strains in which Enzyme I was less sensitive to temperature did not exhibit heat-enhanced regulation. Inhibition was abolished by the crr mutation. The results suggest that Enzyme I functions as a catalytic component of the regulatory system. Simple positive selection procedures are described for the isolation of bacterial mutants which are deficient for either Enzyme I or the heat-stable protein of the phosphotransferase system.
糖磷酸转移酶系统中酶I热不稳定的大肠杆菌突变株,研究了碳水化合物摄取和环腺苷酸3':5'-单磷酸(环AMP)的合成。细胞在非允许温度下孵育导致酶I活性部分丧失,降低了α-甲基葡糖苷的摄取速率和摄取程度。酶I的温度失活还使环AMP合成以及几种碳水化合物(甘油、麦芽糖、蜜二糖和乳糖)的摄取对α-甲基葡糖苷的抑制高度敏感。这些效应似乎不需要蛋白质合成。亲本菌株和酶I对温度不太敏感的“回复突变”菌株未表现出热增强调节。crr突变消除了抑制作用。结果表明,酶I作为调节系统的催化成分发挥作用。描述了用于分离磷酸转移酶系统中酶I或热稳定蛋白缺陷的细菌突变体的简单阳性选择程序。