Photoacoustic spectroscopy of aromatic amino acids in proteins

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.

Acoustic waves from mechanical impulses due to fluorescence resonant energy (Förster) transfer: Blowing a whistle with light

“…This can be explained by the higher force (stress) in eq. (15). Figure 3 also shows that the transient oscillations are larger at the PMMAair interface than at the PMMA-glass interface.…”

“…The physics is related to the photoacoustic effect due to the thermal dilation of a medium in which molecules decay non-radiatively after excitation with light. Photoacoustic spectroscopy has been used to study biomolecular processes such as quantum yields of fluorescent proteins [12], protein folding [13], photosynthesis [14], and fluorophore-DNA binding [15]. The FRET impulse studied here provides an alternative mechanism for generating acoustic waves.…”

Fluorescence and Photoacoustic Spectroscopy-Based Assessment of Mitochondrial Dysfunction in Oral Cancer Together with Machine Learning: A Pilot Study

“…15,16 In comparison, photoacoustic spectroscopy, which is based on the absorption of pulsed light by molecules and subsequent release of heat, generates a transient pressure pulse as acoustic signals, reflecting the molecular properties. 17,18 Therefore, assessing mitochondrial proteins by combining fluorescence and photoacoustic spectroscopy and capturing corresponding spectral signatures of tryptophan in vitro provides a better understanding of the dynamical status of mitochondria. The advantage of this combination is that fluorescence, in contrast to photoacoustic, is sensitive to the scattering loss by the tissue/medium before detection by the detector.…”

“…Hence, it is the most suited molecule for elucidating structural and functional properties by fluorescence, typically associated with membrane proteins. , However, tryptophan fluorescence is sensitive to micro-environmental changes during ligand binding, conformational alterations, protein denaturation, etc., affecting the overall fluorescence intensity. Further, it also shows a shift in the anisotropic properties of proteins upon a change in conformation. , In comparison, photoacoustic spectroscopy, which is based on the absorption of pulsed light by molecules and subsequent release of heat, generates a transient pressure pulse as acoustic signals, reflecting the molecular properties. , Therefore, assessing mitochondrial proteins by combining fluorescence and photoacoustic spectroscopy and capturing corresponding spectral signatures of tryptophan in vitro provides a better understanding of the dynamical status of mitochondria. The advantage of this combination is that fluorescence, in contrast to photoacoustic, is sensitive to the scattering loss by the tissue/medium before detection by the detector.…”

Photoacoustic spectroscopy applied to the direct detection of bioactive compounds in Agaricus brasiliensis mycelium

“…This technique gives information of the optical absorption processes that occur in the material, being also possible to characterize samples regarding to its atomic or molecular composition. In addition, PA spectra can be analyzed through mathematical techniques such as normalizations, derivatives, deconvolutions in Gaussian kernels, and linear regression models [10,11]. Among these techniques, the construction of a linear correlation model employing multivariate analysis methods, such as principal components analysis and partial least squares regression, presents the advantage of building a rigid model, to test it with calibration and validation data, and to obtain information in respect of the sample set dissimilarities.…”