Open AccessPhospho enol pyruvate‐dependent fructose phosphotransferase system in Rhodopseudomonas sphaeroides
Author(s) -
LOLKEMA Juke S.,
ROBILLARD George T.
Publication year - 1985
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1985.tb08720.x
Subject(s) - pep group translocation , phosphorylation , phosphotransferase , periplasmic space , biochemistry , chemistry , vesicle , fructose , membrane , phosphoenolpyruvate carboxykinase , enzyme , escherichia coli , gene
The bacterial phosphotransferase systems are believed to catalyze the concomitant transport and phosphorylation of hexoses and hexitols. The transport is from the outside to the inside of the cell. An absolute coupling between transport and phosphorylation has however been questioned in the literature. We have tested the coupling by analysing the kinetics of fructose phosphorylation by inside‐out vesicles of Rhodopseudomonas sphaeroides . We conclude that fructose indeed has to enter the vesicle before it can be phosphorylated and therefore cannot be phosphorylated from the cytoplasmic side of the membrane. The K m of the phosphorylation reaction is 8 μM. The diffusion of fructose into the vesicle is a reaction that is also catalysed by the compoments of the phosphotransferase system. The undirectional flux from the cytoplasmic side of the membrane to the periplasmic side is a slow process with a K m of 4 mM and is rate‐limiting over a large external fructose concentration range. In summary there is no phosphorylation without transport, but there is transport without phosphorylation.