Structural requirements for binding to the sugar-transport system of the human erythrocyte

Abstract

The structural requirements for binding to the glucose/sorbose-transport system in the human erythrocyte were explored by measuring the inhibition constants, K(i), for specifically substituted analogues of d-glucose when l-sorbose was the penetrating sugar. Derivatives in which a hydroxyl group in the d-gluco configuration was inverted, or replaced by a hydrogen atom, at C-1, C-2, C-3, C-4 or C-6 of the d-glucose molecule, all bound to the carrier, confirming that no single hydroxyl group is essential for binding to the carrier. The binding and transport of 1-deoxy-d-glucose confirmed that the sugars bind in the pyranose form. The relative inhibition constants of d-glucose and its deoxy, epimeric and fluorinated analogues are consistent with the combination of beta-d-glucopyranose with the carrier by hydrogen bonds at C-1, C-3, probably C-4, and possibly C-6 of the sugar. Both polar and non-polar substituents at C-6 enhance the affinity of d-glucose derivatives relative to d-xylose, and d-galactose derivatives relative to l-arabinose, and it is suggested that the carrier region around C-6 of the sugar may contain both hydrophobic and polar binding groups. The spatial requirements at C-1, C-2, C-3, C-4 and C-6 were explored by comparing the relative binding of d-glucose and its halogeno and O-alkyl substituents. The carrier protein closely approaches the sugar except at C-3 in the d-gluco configuration, C-4 and C-6. d-Glucal was a good inhibitor, showing that a strict chair form is not essential for binding. 3-O-(2',3'-Epoxypropyl)-d-glucose, a potential substrate-directed alkylating agent, bound to the carrier, but did not inactivate it.

Acute regulation of glucose transport in a monocyte–macrophage cell line: Glut-3 affinity for glucose is enhanced during the respiratory burst

“…Hence the differences between 2-DOG and 3-O-MG uptake and K m could be explained by the phosphorylation of 2-DOG by hexokinase. Higher K m values were observed when 3-O-MG was used ; this has been reported by other investigators using other cell types [32][33][34][35][36]. Differences in uptake between the two hexoses were also observed and these would have contributed to the differences in V max .…”

Functional Studies of Threonine 310 Mutations in Glut1

“…This hydrophilic amino acid is predicted to be near (5) or at (18) the exofacial end of helix 8, which, in turn, is predicted to be involved in the formation of the water-accessible glucose channel (17,18,35). The threonine hydrophilic side chain with its hydroxyl group may play an important role in forming hydrogen bonds with glucose (36). The T310I mutation substitutes the hydrophobic amino acid isoleucine.…”

Compartmentation of hexokinase in rat heart. A critical factor for tracer kinetic analysis of myocardial glucose metabolism.

“…In both of these steps, the tracer compounds may differ kinetically from glucose (9)(10)(11)(12). It is for this reason that the lumped constant (i.e., the correction factor used to equate 2-deoxyglucose to glucose uptake) must be used to derive rates ofglucose utilization from rates of 2-deoxyglucose uptake and phosphorylation ( 1 ).…”