Photoacoustic spectroscopy of aromatic amino acids in proteins |
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Authors: | Milton Roque Bugs Raquel Kely Bortoleto-Bugs Marinônio Lopes Cornélio |
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Institution: | (1) COGNITUS Project, CENPES/PETROBRAS, Rio de Janeiro, RJ, Brazil;(2) CenPRA, Centro de Pesquisas Renato Archer, Rodovia Dom Pedro I, km 143,6, Bairro Amarais, CEP 13069-901 Campinas, SP, Brazil;(3) Departamento de Física, IBILCE/UNESP, Sao Jose do Rio Preto, SP, Brazil |
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Abstract: | This paper concerns the use of photoacoustic spectroscopy (PAS) to study the presence of aromatic amino acid in proteins.
We examined the aromatic amino acids in six proteins with well-known structures using absorption spectra of near ultraviolet
PAS over the wavelength range 240–320 nm. The fundamental understanding of the physical and chemical properties that govern
the absorption of light and a subsequent release of heat to generate a transient pressure wave was used to test the concept
of monitoring aromatic amino acids with this method. Second derivative spectroscopy in the ultraviolet region of proteins
was also used to study the regions surrounding the aromatics and the percentage area in each band was related in order to
determine the contribution in function of the respective molar extinction coefficients for each residue. Further investigation
was conducted into the interaction between sodium dodecyl sulphate (SDS) and bothropstoxin-I (BthTx-I), with the purpose of
identifying the aromatics that participate in the interaction. The clear changes in the second derivative and curve-fitting
procedures suggest that initial SDS binding to the tryptophan located in the dimer interface and above 10 SDS an increased
intensity between 260 and 320 nm, demonstrating that the more widespread tyrosine and phenylalanine residues contribute to
the SDS/BthTx-I interactions. These results demonstrate the potential of near UV-PAS for the investigation of membrane proteins/detergent
complexes in which light scattering is significant. |
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Keywords: | Photoacoustic spectroscopy Aromatic amino acids Curve-fitting Bothropstoxin-I SDS |
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