Abstract
In a fructose-containing medium in which rye root-microsomal membrane vesicles had reached the equilibrium of uptake of fructose, the presence of both Mg2+ and ATP caused the efflux of fructose from the vesicles. Because the fructose-containing medium did not contain any readily permeant anions, it is unlikely that proton pump-dependent, ΔpH-driven proton/monosaccharide cotransport was the cause of the efflux of fructose. Among nucleotides examined, ATP caused the largest efflux of fructose. The efflux of fructose dependent on Mg2+ and ATP was quite insensitive to a protonophore, CCCP, while it was largely inhibited by vanadate, which inhibits an ATP-binding cassette transporter (glutathione-conjugate pump) of higher plants. It was shown that the Michaelis-Menten constant (Km) of the efflux was 0.4 mM.
