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Structural Stability of Rhodopsin and Opsin Studied by Differential Scanning Calorimetry

  • J. H. McDowell
  • S. M. A. Khan
  • D. W. Bolen
  • M. M. Santoro
  • P. A. Hargrave
Conference paper
Part of the Research Reports in Physics book series (RESREPORTS)

Abstract

The thermal stability of opsin and rhodopsin in disk membranes of bovine retinal rod cell outer segments has been examined by differential scanning calorimetry (DSC). Consistent data is obtained when all parameters of the membrane preparation are carefully reproduced. Calorimetric parameters for opsin and rhodopsin vary as a function of scan rate, membrane concentration and pH. Binding of retinal imparts a stabilization to the protein structure indicated by a temperature of thermal denaturation (Tm) of 71.4ºC for rhodopsin as compared to 55.3°C for opsin. Similarly, the ΔHcal for rhodopsin (167 kcal/mole) is 43 kcal/mole higher than that for opsin (124 kcal/mole). By contrast, a much smaller effect is obtained in samples subjected to limited proteolysis indicating that the membrane-embedded portion of the protein lends quantitatively more stability to the protein than does its cytoplasmic surface. DSC confirms that the pH of maximal stability of both opsin and rhodopsin is 6.1. DSC can be used successfully to examine stability of rhodopsin in detergent solution. In membrane suspensions, membrane-membrane interactions are indicated by a dependence of ΔHcal on the membrane concentration. Intermolecular interactions within the disk membrane are indicated by a dependence of opsin’s ΔHcal on the extent of bleaching of the membrane suspension.

Keywords

Differential Scanning Calorimetry Thermal Denaturation Disk Membrane Differential Scanning Calorimetry Scan Cytoplasmic Surface 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1992

Authors and Affiliations

  • J. H. McDowell
    • 1
  • S. M. A. Khan
    • 2
  • D. W. Bolen
    • 2
  • M. M. Santoro
    • 2
  • P. A. Hargrave
    • 1
    • 3
  1. 1.Department of OphthalmologyUniversity of FloridaGainesvilleUSA
  2. 2.Department of Chemistry and BiochemistrySouthern Illinois UniversityCarbondaleUSA
  3. 3.Department of Biochemistry and Molecular BiologyUniversity of FloridaGainesvilleUSA

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