Kinetics of 3-O-methyl-D-glucose transport in isolated rat hepatocytes

Abstract

3-O-Methyl-D-glucose transport across the plasma membrane of isolated rat hepatocytes was followed for net entry of the sugar into sugar-free cells (zero trans entry), net exit of sugar into sugar-free medium (zero trans exit) and for unidirectional entry and exit fluxes when cells had been equilibrated with sugar in the extracellular medium (equilibrium exchange entry and exit). These measurements were performed at 20 degrees C and pH 7.4 by the use of simple manual methods. Initial rates of transport showed a Michaelis--Menten dependency on the sugar concentration at the cis side of the membrane over the range of concentrations tested (100 microM to 100 mM). Transport was found to be symmetrical with no evidence of substrate stimulation of transport from the trans side of the membrane. Parameters (mean values +/- S.E.M.) of transport were estimated as Vmax. 86.2 +/- 9.7 mmol/litre of cell water per min and Km 18.1 +/- 5.9 mM for exchange entry, Vmax. 78.8 +/- 5.3 mmol/litre of cell water per min and Km 17.6 +/- 3.5 mM for exchange exit, Vmax. 84.1 +/- 8.4 mmol/litre of cell water per min and Km 16.8 +/- 4.6 mM for zero trans exit.

Fructose transporter Glut5 expression in clear renal cell carcinoma

“…Overexpression of the facilitative glucose-transporter has been observed for a wide range of human cancers (41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58) with the degree of overexpression generally being inversely correlated with prognosis. The mechanisms by which GLUTs promote malignant cellular behaviour have focused on factors inducing its expression, such as local hypoxia (37), oncogenes such as Ras, Scr (15) or Myc (38).…”

Molecular changes in the expression of human colonic nutrient transporters during the transition from normality to malignancy

“…Transformation is correlated with a decrease in the expression of GLUT2. GLUT1 has a significantly higher affinity for glucose (Km=1 -2 mM; Wheeler, 1985) than GLUT2 (Km=15 -40 mM; Craik and Elliott, 1979), suggesting that the expression of GLUT1 would allow cells to absorb glucose efficiently at low extracellular concentrations. In colonic tumours expressing low levels of MCT1, the induction of GLUT1 and the down-regulation of GLUT2 would enable the cells to take up and utilise glucose efficiently and ensure their growth and survival in the absence of their conventional energy source, butyrate.…”

Structure of, and functional insight into the GLUT family of membrane transporters

“…14- 16 Kayano et al identified human GLUT3 in 1988. 15 GLUT3 is a 496 amino acid protein and was cloned from a human fetal skeletal muscle cDNA library.…”

“…98,99 However, asymmetric glucose transport activities are not seen in hepatocytes or adipocytes, which are mediated by GLUT2 and GLUT4, respectively. 16,102,103 Several recent investigations also indicate that GLUT1 can form oligomers, such as dimers or tetramers, which could account for the three phases and asymmetric kinetics. [104][105][106][107] Cloherty et al 106 and De Zutter et al 107 proposed that the glucose transporters in mammalian cells present as cooperative dimers or tetramers of GLUT1, and they hypothesized that one (or two in a tetramer) exofacial and one (or two in a tetramer) endofacial hexose binding site(s) present simultaneously.…”