Open AccessHigh‐field phosphorus NMR studies of the stoichiometry of the lactate/proton carrier in Streptococcus faecalis
Author(s) -
SIMPSON Stephen J.,
BENDALL M. Robin,
EGAN Aubrey F.,
VINK Robert,
ROGERS Peter J.
Publication year - 1983
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1983.tb07705.x
Subject(s) - stoichiometry , chemistry , phosphorus 31 nmr spectroscopy , proton , hydrolysis , analytical chemistry (journal) , nuclear magnetic resonance spectroscopy , inorganic chemistry , stereochemistry , chromatography , biochemistry , physics , quantum mechanics
Highfield 31 P‐NMR studies of whole cells of Steptococcus faecalis have shown that ΔpH can be formed by ATP hydrolysis and also by lactate transport. We have used 31 P‐NMR to measure the pH dependence of the variable stoichiometry of the proton/lactate carrier. At low external pH (pH ∼ 6.5) the influx stoichiometry was 1.1 H + /lactate, while at high pH (7.5) the ratio was almost 2; the apparent midpoint pH of this variable stoichiometry is 7. ΔΨ measurements support the electrogenic nature of lactate transport at high pH; the variable rate of membrane depolarization caused by lactate transport also had a midpoint near pH 7.0. The data is consistent with a symmetrical carrier operating with variable stoichiometry as proposed by Michels et al. [(1979) FEMS Microbiol. Lett. 5 , 357–364].