Effects of heating at neutral and acid pH on the structure of beta-lactoglobulin A revealed by differential scanning calorimetry and circular dichroism spectroscopy.
The structural change of beta-lactoglobulin A (betaLG A) on heating was measured at pH 3.0 and 7.5 with UV absorption difference spectra, differential scanning calorimetry (DSC), and circular dichroism (CD). At pH 3.0, betaLG A showed a reversible structural change by heating at 80 degrees C, while an irreversible change was observed and molecular aggregates of betaLG were formed by heating at 95 degrees C. DSC analysis of betaLG A gave endothermic peaks at 75 degrees C and 90 degrees C at pH 7.5, and 90 degrees C at pH 3.0. At pH 7.5, betaLG A modified with N-ethylmaleimide (NEM-betaLG A) gave two endothermic peaks: at 72 degrees C and 90 degrees C. CD spectra of betaLG A heated at various temperatures and pHs were measured and the spectra at pH 3.0 and 7.5 were not changed by heating to 95 degrees C and 80 degrees C, respectively. Unheated NEM-betaLG A gave a spectrum similar to that of heated betaLG A, suggesting that the secondary structure was changed by NEM treatment.
Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan.
Ritsuko
R
Wada
Yuki
Y
Fujita
Naofumi
N
Kitabatake
D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins / Q000737:chemistry*; D011489:Protein Denaturation; D013056:Spectrophotometry, Ultraviolet
D007782:Lactoglobulins