A differential scanning calorimetric study of the influence of copper and dodecyl trimethyl ammonium bromide on the stability of bovine alpha-lactalbumin.
Bovine alpha-lactalbumin (alpha-LA) has been studied by differential scanning calorimetry (DSC), fluorescence spectroscopy and viscometry with various concentrations of Cu2+ and DTAB to elucidate the effect of these ligands on its thermal properties. The DSC profile of dialyzed form of alpha-lactalbumin (m-alpha-LA) contrary to the undialyzed form (holo-form, h-alpha-LA) shows two temperature induced heat absorption peaks. The m-alpha-LA is not a new form of alpha-LA. It contains mixture of the apo (a-alpha-LA) and holo (h-alpha-LA) forms of alpha-LA at low and high temperatures, respectively. Therefore, these two states of alpha-LA (apo and holo) are equilibrating with together after dialyze experiment. The Cu2+ as a metal ion and DTAB as a non metal ion alter the two heat-absorption peaks, in such a manner that, the addition of Cu2+ to the m-alpha-LA increases partial molar heat capacity and enthalpy change values of the h-alpha-LA form at high temperature because the molecular population of the a-alpha-LA form changes into the h-like-alpha-LA. On the contrary, the interaction between the DTAB and the m-alpha-LA increases these thermodynamic values for the a-alpha-LA at low temperature. However, DTAB bound to m-alpha-LA prevents from Ca2+ binding to protein, because there are positive charges repulsion between them. The high temperature peak occurs at the same temperature as the unfolding of the h-alpha-LA, while the low temperature peak lies within the temperature range associated with the unfolding of the a-alpha-LA. The R(s) values of m-alpha-LA, h-alpha-LA and a-alpha-LA forms confirmed the folding and unfolding of the m-alpha-LA during the addition of Cu2+ and DTAB at different concentration, respectively.
Housaindokht
M R
MR
Department of Chemistry, Faculty of Science, Islamic Azad University of Mashhad, Mashhad, Iran.
Chamani
J
J
Moosavi-Movahedi
A A
AA
D000818:Animals; D002152:Calorimetry, Differential Scanning / Q000379:methods*; D002417:Cattle; D003300:Copper / Q000737:chemistry*; D006358:Hot Temperature; D007477:Ions; D007768:Lactalbumin / Q000737:chemistry*; D008024:Ligands; D046911:Macromolecular Substances / Q000737:chemistry; D008956:Models, Chemical; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics
D007477:Ions; D008024:Ligands; D046911:Macromolecular Substances; D000644:Quaternary Ammonium Compounds; C013912:decyltrimethylammonium; D003300:Copper; D007768:Lactalbumin; C022806:dodecyltrimethylammonium