THERMAL-DENATURATION OF DEIONIZED AND NATIVE PURPLE MEMBRANES
THERMAL-DENATURATION OF DEIONIZED AND NATIVE PURPLE MEMBRANES
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DOI：
10.1016/0005-2736(88)90546-9
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发表时间：
1988-08-18
期刊：
影响因子：
--
通讯作者：
PADROS, E
中科院分区：
文献类型：
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作者：
CLADERA, J;GALISTEO, ML;PADROS, E
Spectrophotometric and microcalorimetric techniques have been used to study the influence of cations on the thermal denaturation of bacteriorhodopsin. Deionized (blue) membrane at pH 5.0 shows a lower enthalpy of denaturation than native purple membrane, as well as a denaturation temperature about 20.degree. C lower. Divalent cation binding increases both the temperature and enthalpy of denaturation. pH values also affect thermal denaturation of deionized membrane. At pH 6.5, a denaturation temperature about 20.degree. C higher thatn at pH 4.0 and a much higher enthalpy are obtained. Ultraviolet difference spectra suggest that tryptophan residues are located in more exposed regions in the deionized membrane than in the native membrane. Hg2+, which does not promote the purple form, only slightly affects the temperature and enthalpy of denaturation. The small reversible pretransition observed for native purple membrane at about 80.degree. C, attibuted to a disordering of the lattice distribution of bacteriorhodopsin molecules, is absent in the deionized membrane and in that supplemented either with 1 mol of Mn2+ or 5-20 Hg2+ mol per mol of bacteriorhodopsin. The possible contribution of surface membrane potential and of defined protein conformation to bacteriorhodopsin stability is discussed.
