%0 Journal Article %J Biochemistry %D 2001 %T Effect of temperature, pH, and metal ion binding on the secondary structure of bacteriorhodopsin: FT-IR study of the melting and premelting transition temperatures %A Heyes, C D %A El-Sayed, Mostafa A %X 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. %B Biochemistry %V 40 %P 11819-11827 %8 Oct %@ 0006-2960 %G eng %M WOS:000171400100018 %R 10.1021/bi002594o