TY - JOUR T1 - Effect of temperature, pH, and metal ion binding on the secondary structure of bacteriorhodopsin: FT-IR study of the melting and premelting transition temperatures JF - Biochemistry Y1 - 2001 A1 - Heyes, C D A1 - El-Sayed, Mostafa A AB - We have measured the temperature dependence of the FT-IR spectra of bacteriorhodopsin (bR) as a function of the pH and of the divalent cation regeneration with Ca2+ and Mg2+. It has been found that although the irreversible melting transition shows a strong dependence on the pH of the native bR, the premelting reversible transition at 78-80 degreesC shows very little variation over the pH range studied. It is further shown that the acid blue bR shows a red-shifted amide I spectrum at physiological temperature, which shows a more typical alpha -helical frequency component at 1652 cm(-1) and could be the reason for the observed reduction of its melting temperature and lack of an observed premelting transition. Furthermore, the thermal transitions for Ca2+- and Mg2+-regenerated bR (Ca-bR and Mg-bR, respectively) each show a premelting transition at the same 78-80 degreesC temperature as the native purple membrane, but the irreversible melting transition has a slight dependence on the cation identity. The pH dependence of the Ca2+-regenerated bR is studied, and neither transition varies over the pH range studied. These results are discussed in terms of the cation contribution to the secondary structural stability in bR. VL - 40 SN - 0006-2960 N1 - Heyes, CD El-Sayed, MA M3 - 10.1021/bi002594o ER -