Open AccessThe phospho enol pyruvate‐dependent fructose‐specific phosphotransferase system in Rhodopseudomonas sphaeroide
Author(s) -
LOLKEMA Juke S.,
ten HOEVEDUURKENS Ria H.,
ROBILLARD George T.
Publication year - 1986
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1986.tb09410.x
Subject(s) - phosphoenolpyruvate carboxykinase , chemistry , pep group translocation , fructose , enthalpy , hydrolysis , biochemistry , enzyme , thermodynamics , physics
Energy coupling to fructose transport in Rhodopseudomonas sphaeroides is achieved by phosphorylation of the membrane‐spanning fructose‐specific carrier protein, E Fru II . The phosphoryl group of phospho enol pyruvate is transferred to E Fru II via the cytoplasmic component SF (soluble factor). The standard free enthalpy of hydrolysis of the two phosphorylated proteins has been estimated from isotope exchange measurements in chemical equilibrium. The Δ G ° for SF‐ P is −60.5 kj/mol. The standard free enthalpy for hydrolysis of E II ‐ P is −37.9 kJ/mol, but −45.2 kJ/mol when SF is still complexed to it, as in the overall reaction. Therefore the standard free enthalpy of hydrolysis of SF. E II ‐ P is 70% of the standard free enthalpy of hydrolysis of P ‐ enol pyruvate. The measurements reveal two regulation sites in the system. First, the phosphorylation of SF is inhibited by pyruvate when the concentration ratio of pyruvate/ P ‐ enol pyruvate becomes too high. Second, a low concentration of internal fructose prevents the phosphorylation of the carrier by the internal fructose‐1‐ P pool when the concentration of the latter becomes too high or the phosphorylation rate by P ‐ enol pyruvate too slow. Furthermore comparison of the isotope exchange and the overall phosphotransferase reaction kinetics leads to the conclusion that binding of fructose to the carrier is a slow step relative to the phosphoryl group transfer from E Fru II to fructose.