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Media type:
E-Article
Title:
Substrate specifity of the hexose carrier in the plasmalemma of Chenopodium suspension cells probed by transmembrane exchange diffusion
Contributor:
Gogarten, Johann Peter;
Bentrup, Friedrich-Wilhelm
Published:
Springer-Verlag, 1989
Published in:
Planta, 178 (1989) 1, Seite 52-60
Language:
English
ISSN:
0032-0935;
1432-2048
Origination:
Footnote:
Description:
Substrate specifity of the proton-driven hexose cotransport carrier in the plasmalemma of photoautotrophic suspension cells of Chenopodium rubrum L. has been studied through the short-term perturbation of 14C-labelled efflux of 3-O-methyl-D-glucose. Efflux, occurring exclusively via carrier-mediated exchange diffusion, is trans-stimulated by the substrate and trans-inhibited by the glucose-transport inhibitors phlorizin (${\mathrm{K}}_{\frac{1}{2}}=0.79 \ \mathrm{m}\mathrm{M}$) and its aglucon phloretin (${\mathrm{K}}_{\frac{1}{2}}=84 \ \mathrm{\mu}\mathrm{M}$); with both inhibitors, 3-O-methyl-D-glucose efflux may be blocked completely. Trans-stimulation of efflux (up to fourfold) by a variety of the D-enantiomers of neutral hexoses, including glucose (${\mathrm{K}}_{\frac{1}{2}}=48 \ \mathrm{\mu}\mathrm{M}$), 3-O-methyl-D-glucose (${\mathrm{K}}_{\frac{1}{2}}=139 \ \mathrm{\mu}\mathrm{M}$), and fructose (${\mathrm{K}}_{\frac{1}{2}}=730 \ \mathrm{\mu }\mathrm{M}$), but not by, for instance, D-allose, and L-sorbose, shows that carrier-substrate interaction critically involves the axial position at C-1 and C-3, respectively. We suggest that substrate binding by the Chenopodium hexose carrier involves both hydrophobic interaction with the pyran-ring and hydrogen-ion bonding at C-1 and C-3 of the D-glucose conformation.