Waygood E B, Steeves T
Can J Biochem. 1980 Jan;58(1):40-8. doi: 10.1139/o80-006.
Enzyme I of the phosphoenolpyruvate - sugar phosphotransferase system (PTS) has been purified to homogeneity from Escherichia coli. A merodiploid strain P650 which had an extra copy of the gene for enzyme I resulting in a twofold increase in the amount of activity was used. The enzyme is a dimer of 67 000 +/- 5000 molecular weight subunits. At low protein concentration and 4 degrees C the monomer predominates, while at room temperature the dimer predominates. At higher protein concentrations (2 to 10 mg) this reversible temperature-dependent association-dissociation is not found. Enzyme I has a pH optimum of pH 7.2, a Km for HPr of 9 +/- 3 microM, a Km for phosphoenolpyruvate of 0.18 +/- 0.04 mM, and kinetics that are consistent with a bi bi Ping-Pong mechanism. No allosteric regulation of kinetic activity has been found. The amino acid composition has been determined and the epsilon 1% 280 nm is 4.4. Evidence suggests that the phosphorylated form of enzyme I is more stable.
磷酸烯醇丙酮酸 - 糖磷酸转移酶系统（PTS）的酶I已从大肠杆菌中纯化至同质。使用了一个部分二倍体菌株P650，该菌株具有酶I基因的额外拷贝，导致活性量增加了两倍。该酶是由分子量为67 000±5000的亚基组成的二聚体。在低蛋白浓度和4℃时，单体占主导，而在室温下二聚体占主导。在较高的蛋白浓度（2至10毫克）下，未发现这种可逆的温度依赖性缔合 - 解离。酶I的最适pH为7.2，对组氨酸磷酸载体蛋白（HPr）的Km为9±3微摩尔，对磷酸烯醇丙酮酸的Km为0.18±0.04毫摩尔，其动力学符合双底物双产物乒乓机制。未发现对动力学活性的变构调节。已确定氨基酸组成，其在280纳米处的百分之一消光系数为4.4。有证据表明酶I的磷酸化形式更稳定。
