Characterization of the D-glucose/Na+ cotransport system in the intestinal brush-border membrane by using the specific substrate, methyl alpha-D-glucopyranoside

Biochim Biophys Acta. 1987 Nov 2;904(1):71-80. doi: 10.1016/0005-2736(87)90088-5.


By using isolated membrane vesicles, we have investigated the tenet that D-glucose transport across the intestinal brush-border membrane involves at least two distinct, Na+-activated agencies (D-glucose transport systems S-1 and S-2), only one of which (S-1) can use methyl alpha-D-glucopyranoside (methyl alpha-glucoside) as a substrate. Our results with this glucose analogue show that: (a) As a function of time, methyl alpha-glucoside uptake exhibits a typical overshoot, similar to but smaller than that given by D-glucose with the same vesicle batch. (b) Nonlinear regression analysis of substrate-saturation curves reveals that, contrary to D-glucose, methyl alpha-glucoside transport involves a single transport system which we have identified as S-1. (c) Methyl alpha-glucoside exhibits an apparent affinity (defined as the reciprocal of Km) 4-times smaller than that of D-glucose for S-1 (Km(Dglucose) = 0.5 mM; Km(methyl alpha-glucoside) = 2 mM). However, methyl alpha-glucoside has a Vmax (230 pmol/mg protein per s) identical to that characterizing D-glucose transport by this system. (d) In the absence of Na+, methyl alpha-glucoside uptake is indistinguishable from simple diffusion, confirming that Na+ is an obligatory activator of S-1. (e) Phlorizin behaves as a fully competitive inhibitor of methyl alpha-glucoside transport (Ki = 18 microM), again indicating that S-1 is involved. (f) Neither phloretin nor cytochalasin B affects methyl alpha-glucoside uptake. We conclude that methyl alpha-glucoside is a substrate specific for S-1, which permits study of the properties of this system without interference by substrate fluxes taking place through any other channel.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / drug effects
  • Cytochalasin B / pharmacology
  • Female
  • Glucose / metabolism*
  • Guinea Pigs
  • Intestinal Mucosa / metabolism*
  • Kinetics
  • Male
  • Membrane Potentials
  • Methylglucosides / metabolism*
  • Methylglycosides / metabolism*
  • Microvilli / metabolism
  • Phlorhizin / pharmacology
  • Sodium / metabolism*
  • Sodium / pharmacology


  • Methylglucosides
  • Methylglycosides
  • Cytochalasin B
  • methylglucoside
  • Sodium
  • Phlorhizin
  • Glucose