Laboratory of Biochemistry, B.C.P. Jansen Institute, University of Amsterdam, PO Box 20151, 1000 HD Amsterdam, The Netherlands.
EMBO J. 1983;2(5):715-20. doi: 10.1002/j.1460-2075.1983.tb01490.x.
A hypothesis for the regulation of some sugar transport systems by the bacterial phosphoenolpyruvate:sugar transport system postulates an interaction between III of this system and the carrier whose activity is regulated. We have studied this interaction in more detail, employing one of these transport systems, the lactose carrier of Escherichia coli. Purified III of the phosphotransferase system interacted directly with the lactose carrier. The binding of III to lactose carrier required the presence of the non-phosphorylated form of III and substrates of the carrier and exhibited a stoichiometry of 1.2+/- 0.2 mol III/mol lactose carrier. The K(d) of lactose carrier for III was 10 +/- 5 microM. III is apparently unable to interact with a mutant lactose carrier which still binds but does not transport galactosides. The binding of III to the lactose carrier results in a 3.5-fold increase in the apparent affinity of galactosides for the carrier. Significantly, the binding of III to the lactose carrier results in an inhibition of galactoside translocation both in membrane vesicles and liposomes reconstituted with the purified lactose carrier. This inhibition may thus be the basis for the well-documented phenomenon of inducer exclusion.
糖转运系统调控的假说假设该系统的 III 与受调控的载体之间存在相互作用。我们更详细地研究了这种相互作用，使用了其中一种转运系统，即大肠杆菌的乳糖载体。磷酸转移酶系统的纯化 III 直接与乳糖载体相互作用。III 与乳糖载体的结合需要 III 的非磷酸化形式和载体底物的存在，并表现出 1.2+/- 0.2 mol III/mol 乳糖载体的计量关系。乳糖载体对 III 的 K(d)为 10 +/- 5 microM。III 显然无法与仍能结合但不能转运半乳糖苷的突变型乳糖载体相互作用。III 与乳糖载体的结合导致半乳糖苷对载体的表观亲和力增加了 3.5 倍。重要的是，III 与乳糖载体的结合导致在膜泡和用纯化的乳糖载体重建的脂质体中半乳糖苷的转运受到抑制。这种抑制可能是文献中记载的诱导物排除现象的基础。
