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The asymmetry of the facilitated transfer system for hexoses in human red cells and the simple kinetics of a two component model
Author(s) -
Baker G. F.,
Widdas W. F.
Publication year - 1973
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1973.sp010225
Subject(s) - kinetics , chemistry , asymmetry , affinities , reagent , biophysics , saturation (graph theory) , d glucose , component (thermodynamics) , chromatography , biochemistry , thermodynamics , biology , physics , mathematics , quantum mechanics , combinatorics
1. 4, 6‐ O ‐Ethylidene‐α‐ D ‐glucopyranose (ethylidene glucose) has been used to study the competitive inhibition of glucose exchange fluxes when the reagent was (i) inside the cells and (ii) on the outside. 2. 50% inhibition of glucose exchange at 20 m M and 16° C required 200 m M ethylidene glucose when on the inside in contrast to 25–30 m M when on the outside. 3. The inhibitions at different inhibitor/glucose concentration ratios were measured and analysis of the data suggested that the half‐saturation constant for ethylidene glucose was 6 times that for glucose inside the cell as against 1·5 outside. The analysis, however, suggested an asymmetry in respect to the affinities for glucose of approximately ten‐fold and this would make the asymmetry towards ethylidene glucose forty‐fold. 4. Such asymmetries make it necessary to consider a transfer mechanism for sugars with different components on the outer and inner membrane interfaces and simple kinetics for a two component system have been developed and used for analysing the experimental data quantitatively. 5. The kinetic similarities to and difference from the kinetics of a simple mobile carrier and those of some more recent models are briefly discussed.