Glucose transporter substrate specificity

Interaction between the transported substrate and the carrier was chemically specific, e.g., the carrier could interact with glucose but not with fructose ... 

Gould GW, Thomas HM, Jess TJ, Bell GI (1991), Expression of human glucose transporters in Xenopus oocytes. Kinetic characterization and substrate specificities of the erythrocyte, liver, and brain isoforms, Biochemistry 30 5139-5145. 

GLUT isoforms play a specific role in glucose metabolism determined by their pattern of tissue expression, substrate specificity, transport kinetics and regulated expression in different physiological conditions. 

Unlike Saccharomyces cerevisiae, a strain of Rhodotorula glutinis (gracilis), takes up monosaccharides by unequivocally active transport.203 207 The carrier appears to have wide substrate-specificity, transporting D-fructose, D-galactose, D-glucose, D-mannose, L-rham-nose, D-ribose, D-xylose, and L-xylose. D-Xylose may be concentrated by the cells as much as a thousand-fold.203... 

Figure 7-3 shows that glucose uptake by erythrocytes and liver cells exhibits kinetics characteristic of a simple enzyme-catalyzed reaction involving a single substrate. The kinetics of transport reactions mediated by other types of proteins are more complicated than for uniporters. Nonetheless, all protein-assisted transport reactions occur faster than allowed by passive diffusion, are substrate-specific as reflected in lower Kjn values for some substrates than others, and exhibit a maximal rate (Vjjjax)-... 

Integral proteins are embedded in the membrane itself, to some degree, and are referred to as transmembrane proteins if they extend from one side of the membrane to the other. Typically these proteins have multiple domains or regions that are either primarily hydrophobic, if embedded in the lipid bilayer, or hydrophilic if localized in the extra- or intracellular environment. More complicated tertiary and quaternary protein domain structures allow for the formation of channels or pores where appropriate arrangement of hydrophilic and hydrophobic amino acids on the internal surface of each channel or pore dictates which molecules may enter or bind for subsequent translocation from one side of the membrane to the other. Based on this, some proteins exhibit considerable substrate specificity (e.g., GLUTl a glucose transporter Scheepers et al., 2004) whereas others appear much less specific (e.g., P-glycoprotein Leslie et al., 2005). 

Bovine epithelial cells did not accumulate MG in a specific manner since the uptake was not altered by the presence of Pt, PZ, nor an excess of nonradioactive substrate (Fig. 1). The small accumulation of MG could be related to nonspecific uptake, diffusion, or binding to the cell surface. These results suggest that MAC-T cells grown under the present conditions do not express a Na - dependent glucose transporter. The significant inhibition of uptake of 2-DG by an excess of nonradioactive substrate and by Pt but not by PZ demonstrated that MAC-T cells express one or several Na -independent glucose transporters (Fig. 2). Specific uptake of 2-DG... 

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