Nelson S O, Schuitema A R, Postma P W
Eur J Biochem. 1986 Jan 15;154(2):337-41. doi: 10.1111/j.1432-1033.1986.tb09402.x.
Enzyme IIIGlc of the phosphoenolpyruvate: sugar phosphotransferase system (PTS) of Salmonella typhimurium can occur in two forms: phosphorylated and nonphosphorylated. Phosphorylated IIIGlc (P-IIIGlc) has a slightly lower mobility during sodium dodecyl sulphate/polyacrylamide gel electrophoresis than IIIGlc. In bacterial extracts both phosphoenolpyruvate (the physiological phosphoryl donor of the PTS) as well as ATP can phosphorylate IIIGlc. The ATP-catalyzed reaction is dependent on phosphoenolpyruvate synthase, however, and is due to prior conversion of ATP to phosphoenolpyruvate. The phosphoryl group of phosphorylated IIIGlc is hydrolysed after boiling in sodium dodecyl sulfate but phosphorylated IIIGlc can be discriminated from IIIGlc if treated with this detergent at room temperature. We have used the different mobilities of IIIGlc and P-IIIGlc to estimate the proportion of these two forms in intact cells. Wild-type cells contain predominantly P-IIIGlc in the absence of PTS sugars. In an S. typhimurium mutant containing a leaky ptsI17 mutation (0.1% enzyme I activity remaining) both forms of IIIGlc occur in approximately equal amounts. Addition of PTS sugars such as glucose results, both in wild-type and mutant, in a dephosphorylation of P-IIIGlc. This correlates well with the observed inhibition of non-PTS uptake systems by PTS sugars via nonphosphorylated IIIGlc.
糖磷酸转移酶系统（PTS）的酶IIIGlc可呈现两种形式：磷酸化形式和非磷酸化形式。在十二烷基硫酸钠/聚丙烯酰胺凝胶电泳过程中，磷酸化的IIIGlc（P-IIIGlc）的迁移率略低于IIIGlc。在细菌提取物中，磷酸烯醇丙酮酸（PTS的生理磷酸供体）以及ATP均可使IIIGlc磷酸化。然而，ATP催化的反应依赖于磷酸烯醇丙酮酸合酶，并且是由于ATP预先转化为磷酸烯醇丙酮酸所致。磷酸化的IIIGlc的磷酸基团在十二烷基硫酸钠中煮沸后会水解，但如果在室温下用这种去污剂处理，磷酸化的IIIGlc可与IIIGlc区分开来。我们利用IIIGlc和P-IIIGlc的不同迁移率来估计完整细胞中这两种形式的比例。在没有PTS糖存在的情况下，野生型细胞主要含有P-IIIGlc。在含有渗漏型ptsI17突变（仅保留0.1%的酶I活性）的鼠伤寒沙门氏菌突变体中，两种形式的IIIGlc含量大致相等。添加PTS糖（如葡萄糖）后，无论是野生型还是突变体，P-IIIGlc都会发生去磷酸化。这与观察到的PTS糖通过非磷酸化的IIIGlc对非PTS摄取系统的抑制作用密切相关。
