High D-glucose does not affect binding of alpha-tocopherol to human erythrocytes.
The role of alpha-tocopherol uptake system in human erythrocyte in the uptake of plasma alpha-tocopherol has been suggested. However no information is available on alpha-tocopherol uptake activity of human erythrocytes in the presence of high levels of D-glucose which is known to lead to pathological alterations in different cells including human erythrocytes. Therefore, in order to examine the effect of D-glucose on the binding of alpha-tocopherol to human erythrocytes, the binding characteristics of alpha-tocopherol to these cells were established first. Binding of [3H]alpha-tocopherol to human erythrocytes was both saturable and specific. Scatchard analysis of alpha-tocopherol binding to these cells showed the presence of two independent classes of binding sites with widely different affinities. The high affinity binding sites had a dissociation constant (Kd1) of 90 nM with a binding capacity (n1) of 900 sites per cell, whereas the low affinity binding sites had a dissociation constant (Kd2) of 5.2 microM and a binding capacity (n2) of 105,400 sites per cell. Trypsin treatment abolished all the alpha-tocopherol binding activity. Competition for the binding of alpha-tocopherol to human erythrocytes was effective with other homologues of alpha-tocopherol (beta-tocopherol, gamma-tocopherol and delta-tocopherol) and their potency was almost equal to alpha-tocopherol itself. The order of preference was alpha-tocopherol > beta-tocopherol > or = gamma-tocopherol > or = delta-tocopherol. Incubation of human erythrocytes with various concentrations of D-glucose did not affect alpha-tocopherol uptake activity. Our data demonstrate the presence of an alpha-tocopherol uptake system in human erythrocytes and that the alpha-tocopherol uptake activity is not modulated by the presence of D-glucose.
Bellizzi
M C
MC
Rowett Research Institute, Aberdeen, Scotland, UK.
Dutta-Roy
A K
AK
James
W P
WP
D001665:Binding Sites; D001786:Blood Glucose / Q000502:physiology; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D013379:Substrate Specificity; D014357:Trypsin; D014810:Vitamin E / Q000097:blood*
D001786:Blood Glucose; D014810:Vitamin E; D014357:Trypsin; D005947:Glucose