Protons drive sugar transport through the Na+/glucose cotransporter (SGLT1)

• Published in: The Journal of biological chemistry Vol. 269; no. 34; pp. 21407 - 21410
• Main Authors: Hirayama, B A, Loo, D D, Wright, E M
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 26.08.1994
• Subjects: Animals; Biological Transport; Carrier Proteins - metabolism; Cations - metabolism; Electric Conductivity; Glucose - metabolism; Membrane Glycoproteins; Membrane Proteins - metabolism; Monosaccharide Transport Proteins; Oocytes; Protons; Rabbits; Recombinant Proteins; Sodium - metabolism; Sodium-Glucose Transporter 1; Xenopus laevis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(17)31817-3

Na(+)-dependent transporters, such as the Na+/glucose cotransporter (SGLT1) have long been characterized as having an overwhelming preference for Na+ as the essential ion. We have applied electrophysiological measurements to analyze the ability of protons to transport glucose with a cloned transporter, SGLT1, expressed in Xenopus laevis oocytes. Our results show that protons can drive sugar transport through SGLT1 in the absence of Na+ with the following characteristics: 1) the affinity of SGLT1 for H+ is 3 orders of magnitude higher than its affinity for Na+ (3 microM versus 20 mM); 2) H+ supports a higher maximum transport than Na+, suggesting an alteration in rate-limiting processes; and 3) the cation determines the transporter's affinity for sugar (at Vm = -50 mV, the apparent affinity for alpha-methyl-D-glucoside is 0.2 mM in Na+ and 20 mM in H+). The similarity in the kinetics of H(+)- and Na(+)-dependent sugar transport suggests that the transport mechanism for SGLT1 does not depend on the driving ion.