INTERACTION OF THE INTERDIGITATED DPPG OR DPPG DMPC BILAYER WITH HUMAN ERYTHROCYTE BAND-3 - DIFFERENTIAL SCANNING CALORIMETRY AND FLUORESCENCE STUDIES/

Human erythrocyte band 3 reconstituted into phospholipid vesicles has been used for studying the interaction of interdigitated lipid bilayer with an integral membrane protein. The interdigitated gel phase in DP PG/band 3 or DPPG/DMPC/band 3 systems was induced with polymyxin B (PM B) or Tris+. The phase transitions of the vesicles were detected with high-sensitivity differential scanning calorimetry (DSC). The results indicated that band 3 does not cause significant alterations in the in terdigitated phase of phospholipids, with only a little decrease of th e phase transition enthalpies. Fluorescence measurements showed that t he transition of phospholipid/band 3 systems from the non-interdigitat ed to interdigitated phase is accompanied by marked intrinsic fluoresc ence changes of band 3. The interdigitated phase of DPPG or DPPG/DMPC vesicles increases the intrinsic fluorescence intensity of band 3 and significantly decreases the accessibility of certain tryptophan residu es on the protein to Cs+.