Chemical labelling of arginyl-residues involved in anion transport mediated by human band 3 protein and some aspects of its location in the peptide chain.

The anion exchange system of human red blood cells can be completely inhibited by a large number of arginine-specific reagents. Kinetic studies have shown that these reagents act on the substrate binding site. Complete inhibition of the transport system with 14C phenylglyoxal is accompanied by modification of 2 to 3 arginine residues on the transmembrane segment of band 3. The inhibition and the binding of 14C phenylglyoxal to band 3 is reduced significantly in presence of chloride ions. The interactions between the reversible competitive inhibitor, 4-hydroxy-3-nitrophenylglyoxal (HNPG) and other irreversible anion transport inhibitors with well localized binding sites have been studied. A positive cooperativity between HNPG binding and the inhibition caused by eosin-5-maleimide (EMA), has been measured. Nearly no interactions have been found between HNPG binding site and the histidine residue(s) which react with diethylpyrocarbonate (DEPC). Sulphate self-exchange is irreversibly inhibited by two carboxyl-group reagents, 1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimde (EDC) and N'-(3-dimethylaminopropyl)-N-ethylcarbodiimid methoiodide (EAC), studies on their interaction with the HNPG binding site gave results showing that the reaction site(s) of these reagents do not overlap and are not adjacent to the essential arginine(s). A model concerning such interactions is discussed.