Thermal properties of globulin from rice (Oryza sativa) seeds

The thermal properties of rice (Oryza sativa) seed globulin were studied by differential scanning calorimetry (DSC) under the influence of various medium conditions. The denaturation temperatures (T d) of crude and purified rice globulin were 97.6 and 98.5°C, respectively. Increasing salt concentration enhanced thermal stability of rice globulin. The effect of chaotropic anions on DSC characteristics of rice globulin followed the order of the lyotropic series indicating progressive decreases in both T d and enthalpy (ΔH). Extreme pHs and protein perturbants (sodium dodecyl sulfate at above 20 mM, dithiothreitol, urea and ethylene glycol) caused marked protein denaturation and loss of thermal stability. In contrast, N-ethylmaleimide and SDS at below 20 mM exerted a stabilizing effect on rice globulin. Pre-heat treatments led to partial unfolding of rice globulin, and the level of denaturation increased progressively with increasing heating time. © 2005 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex

Conformational study of globulin from rice (Oryza sativa) seeds by Fourier-transform infrared spectroscopy

The conformation of rice globulin (10%, w/v, in deuterated phosphate buffer, pD 7.4) under the influence of pH, chaotropic salts, several protein structure perturbants and heat treatments was studied by Fourier-transform infrared (FTIR) spectroscopy. Rice globulin exhibited seven major bands in the region of 1700-1600 cm -1 and the spectrum suggests high α-helical content with large quantities of β-sheet and β-turn structures. Highly acidic and alkaline pH conditions induced changes in band intensity attributed to intermolecular β-sheet structure (1681 and 1619 cm -1). Addition of chaotropic salts led to progressive changes in band intensity, following the lyotropic series of anions, whereas several protein structure perturbants caused shifts in band positions. Heating at increasing temperature led to progressive decreases in α-helical content and increases in random coil structures, suggesting protein denaturation. This was accompanied by intensity increases in the intermolecular β-sheet transitions. © 2005 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Raman spectroscopic study of rice globulin

The conformation of rice globulin was studied by Fourier-transform Raman spectroscopy as influenced by different buffer environments and heat treatments. The Raman spectrum of the native protein showed a predominance of α-helical structures as indicated by major amide I and III bands at 1657 and 1270 cm-1, respectively. Highly acidic and alkaline pH conditions induced band shifts and intensity changes in amide I, amide III, and C-H (bending and stretching) vibrations, indicating protein denaturation. Addition of dithiothreitol and β-mercaptoethanol led to changes in S-S stretching vibration, whereas ethylene glycol and urea caused marked changes in tryptophan, tyrosine Fermi doublet and C-H band intensities. Heating at 100°C resulted in progressive denaturation as indicated by band shifts and intensity changes of major spectral regions. Our results revealed that hydrophobic interactions and disulfide bonds play a major role in stabilizing the conformation and in thermal aggregation of rice globulin. © 2005 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex