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J. Biol. Chem., Vol. 265, Issue 29, 17545-17549, Oct, 1990
AJ Jonas and H Jobe
Sulfate transport was examined using membrane vesicles (pH 7.0 inside)
prepared from rat liver lysosomes. Sulfate uptake was dependent upon
external pH with increased uptake at lower buffer pH. The Km for uptake was
160 microM at pH 5.0 while at pH 7.0, a lower affinity system with a Km of
1.4 mM was present. The protonophore carbonyl cyanide m-
chlorophenylhydrazone increased uptake at pH 5.0 while valinomycin/KCl had
no effect. In contrast, at pH 7.0, valinomycin-induced changes in membrane
potential stimulated uptake. Countertransport of sulfate at pH 7.0 was
inhibited by 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene,
N-(4-azido-2-nitrophenyl)-2-aminoethanesulfonic acid, and a variety of
anions: SO4(2-) greater than MoO4(2-) greater than Cl- greater than HPO4-
greater than HCO3-. Trans-stimulation of sulfate uptake at pH 7.0 was
observed with MoO4(2-) and, to a lesser extent, with S2O3(2-) while Cl-,
HPO4-, and HCO3- had little effect. However, chloride loading of vesicles
resulted in marked stimulation of sulfate uptake at pH 5.0. It appears that
sulfate and protons exit lysosomes in exchange for chloride by a specific,
pH-regulated anion transport system.
Sulfate transport by rat liver lysosomes
Department of Pediatrics, Harbor-UCLA Medical Center, Torrance 90502.
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