Interaction of bovine serum albumin (BSA) with ionic surfactants evaluated by electron paramagnetic resonance (EPR) spectroscopy.
EPR spectra of 5- and 16-doxyl stearic acid nitroxide probes (5-DSA and 16-DSA, respectively) bound to bovine serum albumin (BSA) revealed that in the presence of ionic surfactants, at least, two label populations coexist in equilibrium. The rotational correlation times (tau) indicated that component 1 displays a more restricted mobility state, associated to the spin labels bound to the protein; the less immobilized component 2 is due to label localization in the surfactant aggregates. For both probes, the increase of surfactant concentration leads to higher motional levels of component 1 followed by a simultaneous decrease of this fraction of nitroxides and its conversion into component 2. For 10mM cethyltrimethylammonium chloride (CTAC), the nitroxides are 100% bound to the protein, whereas at 10mM N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and sodium dodecyl sulfate (SDS) the fractions of bound nitroxides are reduced to 18% and 86%, respectively. No significant polarity changes were observed in the whole surfactant concentration range for component 1. Moreover, at higher surfactant concentration, component 2 exhibited a similar polarity as in the pure surfactant micelles. For 16-DSA the surfactant effect is different: at 10mM of HPS and CTAC the fractions of bound nitroxides are 76% and 49%, respectively, while at 10mM SDS they are present exclusively in a micellar environment, consistent with 100% of component 2. Overall, both SDS and HPS are able to effectively displace the nitroxide probes from the protein binding sites, while CTAC seems to affect the nitroxide binding to a significantly smaller extent.
de Sousa Neto
Diógenes
D
Instituto de Química de São Carlos, Universidade de São Paulo, Cx. Postal 780, CEP 13560-970, São Carlos, SP, Brazil.
Salmon
Carlos Ernesto Garrido
CE
Alonso
Antonio
A
Tabak
Marcel
M
D000818:Animals; D001665:Binding Sites; D008725:Bis-Trimethylammonium Compounds / Q000737:chemistry; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007477:Ions; D008823:Micelles; D008956:Models, Chemical; D008968:Molecular Conformation; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013113:Spin Labels; D013501:Surface-Active Agents / Q000737:chemistry*
D008725:Bis-Trimethylammonium Compounds; D007477:Ions; D008823:Micelles; D013113:Spin Labels; D013501:Surface-Active Agents; C525618:cethyltrimethylammonium chloride; D012710:Serum Albumin, Bovine; D012967:Sodium Dodecyl Sulfate