Spectroscopic and interfacial properties of myoglobin/surfactant complexes.
The complexes of horse myoglobin (Mb) with the anionic surfactant sodium dodecyl sulfate (SDS), and with the cationic surfactants cetyltrimethylammonium chloride (CTAC) and decyltrimethylammonium bromide (DeTAB), have been studied by a combination of surface tension measurements and optical spectroscopy, including heme absorption and aromatic amino acid fluorescence. SDS interacts in a monomeric form with Mb, which suggests the existence of a specific binding site for SDS, and induces the formation of a hexacoordinated Mb heme, possibly involving the distal histidine. Fluorescence spectra display an increase of tryptophan emission. Both effects point to an increased protein flexibility. SDS micelles induce both the appearance of two more heme species, one of which has the features of free heme, and protein unfolding. Mb/CTAC complexes display a very different behavior. CTAC monomers have no effect on the absorption spectra, and only a slight effect on the fluorescence spectra, whereas the formation of CTAC aggregates on the protein strongly affects both absorption and fluorescence. Mb/DeTAB complexes behave in a very similar way as Mb/CTAC complexes. The surface activity of the different Mb/surfactant complexes, as well as the interactions between the surfactants and Mb, are discussed on the basis of their structural properties.
Tofani
Luca
L
Department of Chemistry, University of Florence, I-50019 Sesto, Florence, Italy.
Feis
Alessandro
A
Snoke
Roy E
RE
Berti
Debora
D
Baglioni
Piero
P
Smulevich
Giulietta
G
D000818:Animals; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D006736:Horses; D046911:Macromolecular Substances / Q000737:chemistry; D008968:Molecular Conformation; D009211:Myoglobin / Q000737:chemistry*; D044367:Phase Transition; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*
D002593:Cetrimonium Compounds; D046911:Macromolecular Substances; D009211:Myoglobin; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; C013912:decyltrimethylammonium; D012967:Sodium Dodecyl Sulfate; D000077286:Cetrimonium