Phosphoenolpyruvate-dependent fructose phosphotransferase system of Rhodopseudomonas sphaeroides: purification and physicochemical and immunochemical characterization of a membrane-associated enzyme I.

The phosphotransferase system (PTS) of the phototrophic bacterium Rhodopseudomonas sphaeroides consists of a component located in the cytoplasmic membrane and a membrane-associated enzyme called "soluble factor" (SF) [Saier, M. H., Feucht, B. U., & Roseman, S. (1971) J. Biol. Chem. 246, 7819--7821]. SF has been partially purified by a combination of hydrophobic interaction and ion-exchange and gel-permeation chromatography. SF is similar to Escherichia coli enzyme I in its molecular characteristics and enzymatic properties. It has a molecular weight of 85 000 and readily dimerizes. Phosphoenolpyruvate and Mg2+ stabilize the dimer. The enzyme catalyzes the conversion of phosphoenolpyruvate into pyruvate and becomes phosphorylated in the process. The phosphoryl group is subsequently transferred to fructose in the presence of R. sphaeroides membranes. SF substitutes for E. coli enzyme I in fructose or glucose phosphorylation with E. coli enzyme II and HPr. The activities of SF with the R. sphaeroides PTS and the E. coli PTS reside on structurally distinct molecules as shown by their response to limited proteolytic digestion and by immunochemical studies. The activity of SF with the E. coli PTS arises during the isolation procedure and is most likely due to the removal of HPr-like protein from SF.