Na+-to-sugar stoichiometry of SGLT3.
Sodium-glucose cotransporters (SGLTs) mediate active transport of sugar across cell membranes coupled to Na+, by using the electrochemical gradient as a driving force. In the kidney, there is evidence for two kinds of cotransporters, a high-affinity, low-capacity system, and a low-affinity, high-capacity system, with differences in substrate specificity and kinetics. Three renal SGLT clones have been identified: SGLT1 corresponding to the high-affinity system, and SGLT2 and SGLT3 with properties reminiscent of the low-affinity system. We have determined the stoichiometry of pig SGLT3 (pSGLT3) by using a direct method, comparing the substrate-induced inward charge to 22Na or [14C]alpha-methyl-D-glucopyranoside uptake in the same oocyte. pSGLT3 stoichiometry is 2 Na+:1 sugar, the same as that for SGLT1, but different from SGLT2 (1:1). The Na+ Hill coefficient for SGLT3 is approximately 1.5, suggesting low cooperativity between Na+ binding sites. Thus SGLT3 has functional characteristics intermediate between SGLT1 and SGLT2, so, whereas SGLT3 stoichiometry is the same as that for SGLT1 (2:1), sugar affinity and specificity are similar to SGLT2.
Díez-Sampedro
A
A
Department of Physiology, University of California Los Angeles, School of Medicine, Los Angeles, California 90095-1751, USA.
Eskandari
S
S
Wright
E M
EM
Hirayama
B A
BA
D027322:Amino Acid Transport System X-AG; D000818:Animals; D002241:Carbohydrates / Q000493:pharmacokinetics*; D002352:Carrier Proteins / Q000378:metabolism*; D050491:Glutamate Plasma Membrane Transport Proteins; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D012965:Sodium Chloride / Q000493:pharmacokinetics*; D051247:Sodium-Glucose Transport Proteins; D051269:Sodium-Glucose Transporter 1; D051297:Sodium-Glucose Transporter 2; D013552:Swine; D027981:Symporters; D014982:Xenopus laevis
D027322:Amino Acid Transport System X-AG; D002241:Carbohydrates; D002352:Carrier Proteins; D050491:Glutamate Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; C495674:SLC5A1 protein, human; C089180:SLC5A2 protein, human; C490298:SLC5A4 protein, human; C495676:Slc5a1 protein, rat; C490300:Slc5a2 protein, rat; D051247:Sodium-Glucose Transport Proteins; D051269:Sodium-Glucose Transporter 1; D051297:Sodium-Glucose Transporter 2; D027981:Symporters; D012965:Sodium Chloride