Characteristics of renal Na(+)-D-glucose cotransport in the skate (Raja erinacea) and shark (Squalus acanthias).
We have investigated the properties of the skate (Raja erinacea) and shark (Squalus acanthias) kidney Na(+)-D-glucose cotransporters (SGLT) in uptake studies of radiolabeled substrates into isolated renal brush-border membrane vesicles (BBMV). Scatchard plot analysis of the substrate dependence revealed that the Na(+)-D-glucose cotransporter population is homogenous within each species. Skate BBMV showed a relatively high affinity for D-glucose [Michaelis constant (K(m)) = 0.12 mM] with an apparent coupling ratio of approximately 2 Na+ to 1 D-glucose, whereas the shark transporter was much lower in affinity (K(m) = 1.90 mM) and had a lower coupling ratio, more like 1 Na+ to 1 D-glucose. These characteristics resemble the properties of SGLT1 and SGLT2, which are known to coexist in the mammalian kidney. Inhibitor studies using sugar analogs and glucosides suggested structural differences of the D-glucose binding site among these transporters, whereas the hydrophobic transporter domains in the vicinity of the D-glucose binding site appeared to be similar. In the high-affinity skate system, D-glucose was recognized by hydrogen bonds to the hydroxy groups at C-2, C-3, and C-4 and by hydrophobic interaction with the C-6 methylene group. In contrast, the low-affinity shark system seemed to lack the hydrophobic recognition motif for the C-6 methylene group of D-glucose.
Kipp
H
H
Max-Planck-Institut für Molekulare Physiologie, Abteilung Epithelphysiologie, Dortmund, Germany.
Kinne-Saffran
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E
Bevan
C
C
Kinne
R K
RK
D000818:Animals; D001665:Binding Sites; D002414:Cations, Monovalent / Q000494:pharmacology; D005260:Female; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D005960:Glucosides / Q000737:chemistry / Q000494:pharmacology*; D006860:Hydrogen Bonding; D007668:Kidney / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D011865:Radioisotope Dilution Technique; D012754:Sharks; D012860:Skates, Fish; D012964:Sodium / Q000378:metabolism*; D051269:Sodium-Glucose Transporter 1; D013045:Species Specificity; D014316:Tritium
D002414:Cations, Monovalent; D005960:Glucosides; D008562:Membrane Glycoproteins; D009004:Monosaccharide Transport Proteins; D051269:Sodium-Glucose Transporter 1; D014316:Tritium; D012964:Sodium; D005947:Glucose