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The effect of α-lactalbumin on the thermotropic phase behaviour of phosphatidylcholine bilayers, studied by fluorescence polarization, differential scanning calorimetry and Raman spectroscopy

Authors
Journal
Biochimica et Biophysica Acta (BBA) - Biomembranes
0005-2736
Publisher
Elsevier
Publication Date
Volume
943
Issue
2
Identifiers
DOI: 10.1016/0005-2736(88)90544-5
Keywords
  • α-Lactalbumin
  • Lipid-Protein Interaction
  • Phosphatidylcholine Bilayer
  • Raman Spectroscopy
  • Fluorescence Polarization
  • Differential Scanning Calorimetry
Disciplines
  • Biology

Abstract

Abstract The effects of bovine α-lactalbumin on the thermotropic properties of dimyristoylphosphatidylcholine liposomes are studied by Raman spectroscopy, fluorescence polarization and differential scanning calorimetry. The Raman spectrum reveals the drastic effects of the protein on the phospholipid structure. The transition temperature shifts downwards and the inter- and intrachain order in the lipid matrix progressively diminish with increasing protein concentration. Up to a lipid to protein molar ratio R = 25, the bilayer structure however is maintained. From fluorescence polarization data we conclude that the protein restricts the mobility of the DPH probe. In view of the Raman results, the lower probe mobility obviously cannot be associated with a more rigid lipid matrix. Nevertheless the transition temperatures of the α-lactalbumin-phospholipid complex increases. DSC measurements give no decisive way out for this discrepancy. These results confirm that different types of lipid order are involved in lipid-protein interactions. Compared to the free protein, the α-helicity of the protein has increased in the complex.

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