Source of transport site asymmetry in the band 3 anion exchange protein determined by NMR measurements of external Cl- affinity

Biochemistry
D LiuP A Knauf

Abstract

Flux measurements indicate that a far greater number of unloaded band 3 anion transport sites face the cytoplasm than face the external medium, but the reason for this striking asymmetry has remained obscure. To resolve this question, we have measured the apparent Cl- affinity of the transport site of human red blood cell band 3 protein under various conditions by analyzing the 35Cl NMR free induction decay (FID). The [Cl-] that half-saturates the transport sites with [Cli] = [Clo] (K1/2) in RBC membranes (ghosts) is 46 +/- 5 mM at 0 degree C, while the Ko1/2 (for half-saturation with [Clo] at constant [Cli]) of intact cells is 3.2 +/- 2.1 mM. When cells were pretreated with EM, an inhibitor of band 3 anion exchange that does not prevent Cl- binding to the external transport site, K1/2 and Ko1/2 are 41 +/- 14 and 46 +/- 12 mM, respectively. The EM-induced increase in Ko1/2 with little change in K1/2 can be most simply interpreted as meaning that EM abolishes the effects of the translocation rate constants on Ko1/2 so that Ko1/2 and K1/2 of EM-treated cells now both reflect the true dissociation constant for binding of Cl- to the external transport site, Ko. The fact that Ko for a slowly transported anion, iodide, is nearly the ...Continue Reading

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Citations

May 22, 2003·The International Journal of Biochemistry & Cell Biology·Anthony D Maher, Philip W Kuchel
Aug 1, 2002·Proceedings of the National Academy of Sciences of the United States of America·Philip A KnaufMartha L Perez
Dec 7, 2007·Biophysical Journal·S A NiedererR D Vaughan-Jones
Apr 10, 2016·Biochimica Et Biophysica Acta·Reinhart A F ReithmeierSo Iwata
Dec 18, 2007·Journal of Theoretical Biology·Andrey V ChernyshevValeri P Maltsev
Sep 25, 1999·Journal of Magnetic Resonance·R Kemp-HarperS Wimperis
Apr 8, 2015·The Journal of Biological Chemistry·Tiziana VigliaroloElena Zocchi
Jul 15, 2000·American Journal of Physiology. Renal Physiology·A M Weinstein
Jul 18, 2001·American Journal of Physiology. Renal Physiology·H Chang, T Fujita

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