Adenosine and adenosine triphosphate modulate the substrate binding affinity of glucose transporter GLUT1 in vitro.
Evidence indicates that a large portion of the facilitative glucose transporter isoform GLUT1 in certain animal cells is kept inactive and activated in response to acute metabolic stresses. A reversible interaction of a certain inhibitor molecule with GLUT1 protein has been implicated in this process. In an effort to identify this putative GLUT1 inhibitor molecule, we studied here the effects of adenosine and adenosine triphosphate (ATP) on the binding of D-glucose to GLUT1 by assessing their abilities to displace cytochalasin B (CB), using purified GLUT1 in vesicles. At pH 7.4, adenosine competitively inhibited CB binding to GLUT1 and also reduced the substrate binding affinity by more than an order of magnitude, both with an apparent dissociation constant (K(D)) of 3.0 mM. ATP had no effect on CB and D-glucose binding to GLUT1, but reduced adenosine binding affinity to GLUT1 by 2-fold with a K(D) of 30 mM. At pH 3.6, however, ATP inhibited the CB binding nearly competitively, and increased the substrate binding affinity by 4--5-fold, both with an apparent K(D) of 1.22 mM. These findings clearly demonstrate that adenosine and ATP interact with GLUT1 in vitro and modulate its substrate binding affinity. They also suggest that adenosine and ATP may regulate GLUT1 intrinsic activity in certain cells where adenosine reduces the substrate-binding affinity while ATP increases the substrate-binding affinity by interfering with the adenosine effect and/or by enhancing the substrate-binding affinity at an acidic compartment.
The Biophysics Laboratory, VA Medical Center, and the Department of Physiology and Biophysics, SUNY at Buffalo School of Medicine and Biomedical Sciences, 3495 Bailey Avenue, Buffalo, NY 14215, USA.
M
M
Lachaal
R A
RA
Spangler
C Y
CY
Jung
D000241:Adenosine / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D003571:Cytochalasin B / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D051272:Glucose Transporter Type 1; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008433:Mathematics; D009004:Monosaccharide Transport Proteins / Q000737:chemistry* / Q000502:physiology; D011485:Protein Binding / Q000187:drug effects; D013379:Substrate Specificity
D051272:Glucose Transporter Type 1; D009004:Monosaccharide Transport Proteins; D003571:Cytochalasin B; D000255:Adenosine Triphosphate; D005947:Glucose; D000241:Adenosine