Membrane vesicles of Streptococcus lactis were used to characterize a novel anion exchange involving phosphate and sugar 6-phosphates. For vesicles loaded with 50 mM phosphate at pH 7, homologous phosphate:phosphate exchange had a maximal rate of 130 nmol/min/mg of protein and a K(t) of 0.21 mM external phosphate; among phosphate analogues tested, only arsenate replaced phosphate. Heterologous exchange was studied by 2-deoxyglucose 6-phosphate entry into phosphate-loaded vesicles; this reaction had a maximal velocity of 31 nmol/min/mg of protein and a K(t) of 26 μM external substrate. Sugar phosphate moved intact during this exchange, since its entry led to internal 32Pi without transfer of 32P to sugar phosphate. Inhibitions of phosphate exchange suggested that the preferred sugar phosphate substrates were (K(iapp)): glucose, 2-deoxyglucose, and mannose 6-phosphates (approximately 20 μM) > fructose 6-phosphate (150 μM) > glucosamine 6-phosphate (420 μM) > α-methylglucoside 6-phosphate (740 μM). Stoichiometry for phosphate:2-deoxyglucose-6-phosphate antiport was 2:1 at pH 7, and since initial rates of exchange were unaffected by charge carrying ionophores (gramicidin, valinomycin, a protonophore), this unequal stoichiometry indicated the electroneutral exchange of two monovalent phosphates for a single divalent sugar phophate.
|Original language||English (US)|
|Number of pages||10|
|Journal||Journal of Biological Chemistry|
|State||Published - Dec 1 1984|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology