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Structural and interaction properties of β‐Lactoglobulin as studied by FTIR spectroscopy
Author(s) -
Lefèvre Thierry,
Subirade Muriel
Publication year - 1999
Publication title -
international journal of food science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.831
H-Index - 96
eISSN - 1365-2621
pISSN - 0950-5423
DOI - 10.1046/j.1365-2621.1999.00311.x
Subject(s) - dipalmitoylphosphatidylcholine , chemistry , monomer , intermolecular force , protein aggregation , crystallography , denaturation (fissile materials) , circular dichroism , fourier transform infrared spectroscopy , phase (matter) , spectroscopy , membrane , phospholipid , molecule , chemical engineering , organic chemistry , polymer , biochemistry , nuclear chemistry , phosphatidylcholine , quantum mechanics , physics , engineering
Summary New aspects of β‐Lactoglobulin (BLG) structure which have not previously been found by FT–IR spectroscopy are presented. The conformational changes of BLG and its heat‐induced denaturation have been studied at low concentration and different pHs. First, it was found that the spectra of BLG in solution are concentration‐dependent. Below 1%, they reveal one component in the 1620–1635 cm −1 region while above this concentration, two components are present. These changes are related to the modifications of the quaternary structure of BLG, i.e. to the monomeric or dimeric forms. As shown at high temperature (85 °C), this concentration (1%) represents the threshold of protein aggregation. Second, the thermal behaviour of BLG at pH 7.4 and 4.4 is compared. The results suggest that the denaturation process and the intermolecular interactions in aggregates are different and lead to two types of aggregate. These observations are in agreement with the formation of two gel microstructures near neutral pH and near the pI of BLG as observed by Stading & Hermasson (1990). Finally, interactions between BLG and two zwitterionic phospholipids have been investigated. Dipalmitoylphosphatidylcholine (DPPC) is unaffected in the presence of BLG, suggesting that no interaction occurs. In contrast, BLG increases the lipid chain conformational disorder of milk sphinglomyelin (SM) as a consequence of hydrophobic interactions of BLG with SM. Since this effect occurs at and above the gel‐to‐liquid‐crystalline phase transition, it is suggested that membrane fluidity plays an important role in these interactions.