| Abstract
| - We have shown that diethyl pyrocarbonate (DEPC) inhibits band 3-mediated anion exchangeand that the inhibition occurs only when histidine residue(s) is (are) modified with DEPC from the cytosolicsurface of resealed ghosts [Izuhara et al. (1989) Biochemistry28, 4725−4728]. In the present study, wehave identified the DEPC-modified histidine residue as His834 using liquid chromatography withelectrospray ionization mass spectrometry (LC/ESI-MS). This mild, rapid, sensitive, and quantitative methodwas successfully applied to analysis of the unstable DEPC−histidine adduct. The DEPC modification ofHis834 was pH dependent and 4,4‘-dinitrostilbene-2,2‘-disulfonic acid (DNDS) sensitive as previouslyshown. After DEPC modification, band 3-mediated anion exchange is inhibited. Consistent with previousresults, we confirmed that His834 was located on the cytosolic side of the membrane and the DEPCmodification of His834 had allosteric effects on the extracellular DNDS-binding site of band 3. Therefore,we conclude that His834 is located at the cytosolic surface of band 3 and is an essential residue for band3-mediated anion exchange. We will discuss important roles of the region from TM12 to TM14 in theconformational changes that occur during the band 3-mediated anion exchange.
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