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Scientific Report 2007-2009
Condensed matter physics and biophysics
C27. FT-IR spectroscopy of proteins
A. Nutritionally relevant proteins. A novel research
line has recently been developed, aimed at the
evaluation of the relationship between structural properties
of proteins of nutritional relevance, as examined
by FT-IR spectroscopy, and nutrient utilization. This
research is in collaboration with the Istituto Nazionale
di Ricerca per gli Alimenti e la Nutrizione (scientific responsible
M. Carbonaro). Fourier-Transform InfraRed
(FT-IR) spectroscopy has been recognized to have several
advantages over other spectroscopic techniques for
the study of proteins in biological systems. In particular,
structure of food proteins with low solubility, such as
plant proteins in denatured states, has been successfully
determined by FT-IR [1]. The secondary structure of
plant and animal proteins of nutritional relevance have
been studied by Diffuse Reflectance FT-IR spectroscopy
(DRIFTS). The results obtained on several proteins with
different structures have been validated by a comparison
with X-ray crystallographic and IR/Raman semiquantitative
data available from the literature.
absorption (a. u.)
1.2
0.9
0.6
0.3
0.8
0.6
0.4
0.2
0.0
1500
beta-sheet
alpha -helix
turn
aggregates
aggregates
1550 1600 1650
energy (cm -1 )
1700
a
b
1750
β-sheet structures have been quantified [2].
Application to legume seed flour analysis allowed to
monitor changes in protein secondary structure that occurred
upon heat processing of increasing intensity. Results
have indicated that high amounts of multimeric
complexes are formed from food proteins of plant origin
with different mechanisms, depending on the initial
content in β-sheet structure. Moreover, the higher the
content in β-sheet structure, the higher was the stability
of the complexes: this feature is likely to adversely affect
protein utilization and may represent a detrimental
factor on the overall nutritional quality [3].
B. Infrared Spectroscopy of Immobilized Enzymes
on Nanostructured Polymers. Enzymes
are biomolecules that catalyze the chemical reactions.
Almost all processes in a biological cell need enzymes to
occur at significant rates and biodegradable polymers
such as poly(lactic acid) may often be utilized as drug
delivery systems because their degradation products
are metabolized in the human body. Suitable enzyme
delivery supports should maintain a high level of enzyme
activity, while preventing a possible leaching out during
the reaction. Particles of nanoscopic size are very
well-suited for the immobilization of enzymes as they
provide large surface areas. In this research we have
investigated Lipase which increases its specific activity
when is immobilized on nanostructured polymers. We
have shown by FT-IR spectroscopy through the study of
amideI-II lipase bands, that this activity enhancement
can be related to a modification of the α/β ratio [4].
Further investigations will be dedicated to improve the
specific activity of Lipase, linking the α/β ratio to the
size of the nano polymer.
References
1. A. Barth, Biochim. Biophys. Acta 1767, 1073 (2007)
2. M. Carbonaro, et al., FEBS J. 276(S1), 274 (2009).
3. M. Carbonaro, et al., Food Chem. 108, 361 (2009).
4. A. Perla et al., Colloids Surf., B64, 56 (2008).
Authors
A. Nucara, P. Maselli, G. Kamel, F. Bordi, S. Lupi
Figure 1: Absorption spectrum of Concanavalin A in the
region of the Amide I. Panel(a): Fourier self- deconvolved
amide band. Panel(b): single Gaussian contributions.
The same procedure has been applied to analysis of
proteins in whole food matrix, and differences in the
secondary structure of proteins between untreated and
processed foods have been detected. Besides to major
amide I contributions: β-sheets (1633-1638 cm −1 ), random
coil (1649 cm −1 ), α-helix (1654-1658 cm −1 ) and β-
turns modes (1671-1678 cm −1 ), minor contributions at
1606-1620 cm −1 and 1690-1696 cm −1 from antiparallel
Sapienza Università di Roma 80 Dipartimento di Fisica