Study of conformation of vicilin from Dolichos lablab and Phaseolus calcaratus by Fourier-transform infrared spectroscopy and differential scanning calorimetry

Fourier-transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) were used to monitor changes in the secondary structure and thermal stability of vicilin from Dolichos lablab (DLV) and Phaseolus calcaratus (PCV) under different environmental conditions. The IR spectra of DLV and PCV in the amide I′ region (1700–1600 cm−1) showed that β-sheets and β-turns were the major secondary structures. Highly acidic and alkaline pH conditions induced changes in the secondary structure. DSC thermograms showed that raising pH from near neutrality decreased denaturation temperature (Td) and enthalpy of denaturation (ΔH). Chaotropic salts (1.0 M) caused a transition from β-sheet to random coil structures, and their effects on thermal stability followed the lyotropic series of anions. Addition of several protein structure perturbants caused changes in IR band intensities and DSC thermal characteristics, indicating protein denaturation.