Two-Dimensional Near-Infrared Correlation Spectroscopy Studies
on Protein Denaturation
Kouichi MURAYAMA, Yan WANG†, Roumiana TSENKOVA and Yukihiro OZAKI*†
Department of Environmental Information and Bio-production Engineering, Faculty of Agriculture, Kobe University; Rokkoudai, Nada-ku, Kobe-shi 657-8501 Japan
† Department of Chemistry, School of Science, Kwansei-Gakuin University; Uegahara, Nishinomiya-shi 662-8501 Japan
We have studied thermal and acid denaturation of ovalbumin by use of generalized two-dimensional (2D) near-infrared (NIR) correlation spectroscopy. NIR spectroscopy provides unique information about the hydration and structure of proteins which infrared and Raman spectroscopy do not offer. However, there observed a number of bands due to overtones and combination modes in the NIR region, so that spectral analysis in the NIR region is not always straightforward. Thus, we have employed 2D correlation spectroscopy to analyze the NIR spectra. By using 2D correlation analysis we have been able to separate bands due to water and protein amide groups. We have calculated synchronous and asynchronous correlation spectra of ovalbumin aqueous solutions by use of its concentration as the perturbation from 45 °C to 80 °C at an interval of 2 °C and from pH 5.8 to pH 2.4 at an interval of pH 0.2. The 2D correlation analysis have suggested that the sudden change in the hydration around 68 °C causes the unfolding process of the secondary structure and that in the acid denaturation the hydration changes markedly around pH 3.0, leading to the gelation. Our studies have demonstrated that 2D correlation NIR spectroscopy holds considerable promise in the studies of hydration and secondary structure change of proteins.
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