PROTEIN CHEMISTRY AND BIOCHEMICAL STUDY ON THE ANION TRANSPORT SYSTEM IN HUMAN ERYTHROCYTE MEMBRANES.

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A human erythrocyte band 3 peptide, affinity labeled with pyridoxal phosphate, was purified by a combination of gel permeation and reverse-phase high performance liquid chromatography. The amino acid sequence of the transmembrane peptide was determined by sequencing subfragments of the peptide obtained from lysyl endopeptidase and staphlococcal proteinase V8 digestions.When a peptide containing the COOH-terminal of human erythrocyte Band 3 was also purified and sequenced, the affinity-labeled peptide was found to be located close to the COOH-terminal of Band 3, where it could be aligned with amino acid residues 852-927 of a murine erythrocyte Band 3, deduced from a nucleotide seguence of a cDNA clone. The amino acid sequence of the COOH-terminal region was highly homologous to that of murine Band 3.As a result, the sequence of the COOH-terminal peptide of band 3 was established as follows. H^^1LFTGIQIIX^^<10> LAVLWVVKST^^<20> PASLALPFVL^^<30> ILTVPLRRVL^^<40> LPLIF RNVEL^^<50> QCLDADDAKA^^<60> TFDEEEGRDE^^<70> YDEVAMPV^^<78>The pyridoxal phosphate binding site was identified as Lys-18 which corresponded to Lys-869 of the deduced sequence. It appears that the COOH-terminal region of band 3 constitutes at least a part of the active center for anion transport in human erythrocyte membrans.Diethylpyrocarbonate inhibited the phosphate exchange across the human erythrocyte membrane. The exchange rate was inhibited only when the membranes were modified with the reagent from the cytosolic surface of resealed ghosts. The intracellular modification by diethylpyrocarbonate inhibited the extracellular binding of [^3H@]-DIDS to Band 3 protein. Furthermore, the extracellular DNDS protected the membranes from the intracellular modification by diethylpyrocarbonate.The sequenced COOH-terminal peptide closely related to the DIDS binding site. Thus, the intracellular modification by diethylpyrocarbonate may transmembranously change the conformation of the COOH-terminal peptide.