Scanning Calorimetry and Fourier-Transform Infrared Studies into the Thermal Stability of Cleaved Bacteriorhodopsin Systems

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• 作者：Ana I. Azuaga ; Francesc Sepulcre ; Esteve Padró ; s ; and Pedro L. Mateo
• 刊名：Biochemistry
• 出版年：1996
• 出版时间：December 17, 1996
• 年：1996
• 卷：35
• 期：50
• 页码：16328 - 16335
• 全文大小：464K
• 年卷期：v.35,no.50(December 17, 1996)
• ISSN：1520-4995

文摘

Differential scanning calorimetry and Fourier-transform infraredspectroscopy have been usedto characterize the thermal stability of bacteriorhodopsin (BR) cleavedwithin different loops connectingthe helical rods. The results are compared to those of the nativeprotein. We show that the denaturationtemperature and enthalpy of BR cleaved at peptide bond 71-72 or155-156 are lower than those of theintact protein, and that these values become even lower for the BRcleaved at both peptide bonds. Theeffect of cleavage on the denaturation temperature and enthalpy valuesseems to be additive as has beenpreviously suggested [Khan, T. W., Sturtevant, J. M., & Engelman, D.M. (1992) Biochemistry 31, 8829].The thermal denaturation of all the samples was irreversible andscan-rate dependent. When cleaved atthe 71-72 bond BR follows quantitatively the predictions of thetwo-state kinetic model at pH 9.5, withan activation energy of 374 kJ/mol, similar to that of native BR.Calorimetry experiments with differentpopulations of intact and cleaved BR provide direct evidence for someintermolecular cooperativity upondenaturation. The denatured samples maintain a large proportion oflpha.gif" BORDER=0> helices and le"> structure, a factwhich seems to be related to their low denaturation enthalpy ascompared to that of water-soluble, globularproteins.