Complex effects of papain on function and inhibitor sensitivity of the red cell anion exchanger AE1 suggest the presence of different transport subsites.
Band 3 (AE1), the anion exchanger of the human erythrocyte membrane, mediates not only fluxes of small hydrophilic anions (e.g., chloride, oxalate), but also the flip-flop of long-chain amphiphilic anions (e.g., dodecylsulfate). Treatment of erythrocytes with papain, long known to inhibit the transport of the former type of anions, accelerates the transport of the latter type. In an attempt to elucidate the basis of these opposite responses to papain, several small amphiphilic arylalkyl sulfonates and -sulfates were tested for the response of their transport, via AE1, to papain. Although all these probes are most likely transported by a flux and not by flip-flop, their transport was inhibited by papain only in some cases, but accelerated in others. Different responses to papain therefore most likely do not reflect differences between transport by flux or by flip. The transports of different species of anions also differed considerably in the changes of their sensitivity, to noncovalent and some covalent inhibitors, brought about by papain treatment. While oxalate transport remained as sensitive as in native cells, transports of small amphiphilic anions lost their sensitivity to a major extent, regardless of the inhibition or acceleration of their transport by papain. The results are discussed in the light of present concepts of the structural organisation of AE1, and interpreted in terms of a model of different transport subsites for different species of anions in this transporter.
St Voswinkel
Institut für Physiologie, Medizinische Fakultät der RWTH Aachen, Universitätsklinikum, Aachen, Germany.
Haest
C W
CW
Deuticke
B
B
D001457:Anion Exchange Protein 1, Erythrocyte / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000378:metabolism*; D000838:Anions; D017920:Antiporters / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000378:metabolism*; D001665:Binding Sites; D027963:Chloride-Bicarbonate Antiporters; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D008958:Models, Molecular; D010206:Papain / Q000494:pharmacology*; D013501:Surface-Active Agents / Q000493:pharmacokinetics
D001457:Anion Exchange Protein 1, Erythrocyte; D000838:Anions; D017920:Antiporters; D027963:Chloride-Bicarbonate Antiporters; D013501:Surface-Active Agents; D010206:Papain