Open AccessEvidence from Electron Paramagnetic Resonance for Function‐Related Conformation Changes in the Anion‐Transport Protein of Human Erythrocytes
Author(s) -
GINSBURG Hagai,
O'CONNOR Sally E.,
GRISHAM Charles M.
Publication year - 1981
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1981.tb05177.x
Subject(s) - electron paramagnetic resonance , band 3 , chemistry , ion , electron transport chain , covalent bond , ion transporter , resonance (particle physics) , vesicle , spin label , crystallography , chloride , nuclear magnetic resonance , membrane , membrane protein , biochemistry , organic chemistry , physics , particle physics
The erythrocyte membrane protein involved in anion transport (band 3) wits isolated in its native lipid milieu in the form of leaky vesicles and then was spin‐labelled with N ‐(1‐oxyl‐2,2,6,6‐tetramethyl‐4‐piperidinyl)‐maleimide (MalMe 4 PipO). The resulting electron paramagnetic resonance spectrum of band‐3‐bound MalMe 4 PipO was resolved into rapid tumbling component and another, relatively immobile component. The percentage of the signal contributed by the mobile component ( Q ), was sensitive to various characteristic factors known to affect erythrocyte anion transport: Q was a hyperbolic function of chloride concentration displaying a half saturation constant K 1/2 similar to that of chloride transport. On the other hand Q showed a biphasic response to sulfate concentration, in line with the relatively high affinity of sulfate for the anion modifier site. Q was a saturable function of pH, either in presence of Cl − or SO −2 4 , showing a p K a between pH 6.0 and 6.5, in analogy with the pH titration curve of Cl − and SO −2 4 transport. Spin‐labelled vesicles treated with a covalent inhibitor of anion transport, 4‐acetamido‐4′‐isothiocyanostilbene‐2,2′‐disulfonic acid, were markedly less susceptible to changes in CI − concentration. It is suggested that the electron paramagnetic resonance spectrum of MalMe 4 PipO covalently bound to the band‐3 protein, reports conformational changes which are related to the anion‐transport function of this protein.