Conformational Specificity in a Biological Sugar Transport System

Abstract

The ‘carrier’ system in the surface of the human erythrocyte, facilitating passage of monosaccharides through the cell membrane, reacts preferentially with those sugars in which the pyranose ring tends to assume the particular ‘chair’ shape designated by Reeves as the ‘C1’ conformation. This novel type of steric specificity was revealed in a comparative study of fourteen aldoses (6 pentoses, 5 hexoses, and 3 deoxyhexoses), in which the dissociation constants of the carrier-sugar complexes were derived from the kinetics of the transfer process and of the competitive inhibition by phloretin. The sequence of increasing affinities thus determined paralleled the sequence of increasing relative stability in the C1 conformation as dictated by the distribution of substituent groups between axial and equatorial positions on the ring. Sugars predominantly stable in the other chair conformation (1C) showed extremely low affinity. Since no instance of biological utilization of the latter sugars has apparently yet been found, it is suggested that the necessity for the C1 ring-shape is basic in all enzymic reactions with pyranoses. However, most systems show further special requirements for particular side-group arrangements, which are superimposed on the primary ring specificity seen in the red cell's sugar transport system.

Glucose Transport into Spinach Chloroplasts

“…Furthermore, the 3H2O-sorbitol space is not significantly altered. Since the 3H20- The specificity of the glucose transport in spinach chloroplasts shows striking similarities to the specificity of the glucose transport in human erythrocytes (15) and in rat liver cells (1). Also, the Km and the activation energy in erythrocytes (8 mm [15], 20 kcal/mol [19]) and in liver cells (30 mm, 22 kcal/mol [1]) are very similar to the values reported here.…”

Structural Requirements of Sugars as Antagonists of the Vascular Response to Dextran in Rat Skin

“…In the present work, however, the structural requirements of sugars for antagonism of the dextran response do not correspond with those of any known transport system. The systems investigated include the penetration of sugars into muscle cells (Battaglia & Randle, 1959 and human erythrocytes (LeFevre & Marshall, 1958), and active transport in the intestine (Cori, 1925;Crane, 1960;Rosenberg, 1961;Wilbrandt & Rosenberg, 1961). Some of the sugars which increase the potential or support fluid transfer across the intestinal wall (Barry, Dikstein, Matthews, Smyth & Wright, 1964) also differ from those which are potent antagonists of the dextran response.…”

Two-compartment model for determination of glycolytic rates of solid tumors byin vivo13C NMR spectroscopy

“…Spectral acquisitions commenced with a control 31 P NMR spectrum obtained during perfusion of cells with growth medium supplemented with 11 mM glucose (at isotopic natural abundance) and 5% FBS. The perfusion reservoir was then switched to D-PBS buffer containing 11 mM of uniformly labeled (UL) 13 C-D-glucose (36.6 atom %, Isotec), and a series of 13 C NMR spectra was acquired over 13 h. A final 31 P NMR spectrum was obtained at the end of this period to check the viability of cells. For determination of lactate production rate, cells were perfused with 11 mM [1-…”