LOCAL STRUCTURAL DIFFERENCE BETWEEN HUMAN AND BOVINE BAND-3 IN THE ANION TRANSPORT INHIBITOR-BINDING REGION

We have examined molecular properties of inhibitor-complexed human and bovine band 3, an anion transport protein of erythrocyte membrane, in order to demonstrate the structural characteristics of the inhibitor binding region, Band 3 modified with DIDS (4,4'-diisothiocyano-2,2'-st ilbenedisulfonate), a potent anion transport inhibitor, generated a po sitive circular dichroic band at a wavelength of 345 nm, corresponding to a DIDS chromophore. The dichroic spectra of human band 3-DIDS comp lex and its bovine counterpart differed markedly in their ellipticity, Under the conditions that H2DIDS (the dihydro-derivative of DIDS) cro ss-linked two chymotryptic fragments of human band 3, the reagent fail ed to cross-link the equivalent bovine fragments, The inhibitory effec t of PLP (pyridoxal 5'-phosphate), a substrate and affinity label, on phosphate influx into red blood cells was more pronounced for human ba nd 3 than for bovine band 3, The residue Lys-562 of human band 3 was f ound to be modified with PLP, while the corresponding residue of bovin e band 3 was devoid of reactivity with PLP.