Studies on components 1' (modified monomer) and 2 (dimer) formed during heat-treatment of bovine serum albumin

Abstract

When the solution of bovine serum albumin at pH 9 is incubated at 65 °C, new components 1' (modified monomer), 2 (dimer) and 3 (probably trimer) are formed. The isoelectric focusing indicated that the isoelectric points of components 1', 2 and 3 were pH 5.9.

The hydrogen ion titration curve for the native albumin had well known abnormal steepness at pH near 4, but that for component 1' had no abnormal steepness. The titration curve for component 1' located right side of that for the native albumin.

Circular dichroism measurements indicated that some unfolding occurred, when the native albumin was changed to component 1'. The contents ofα-helix were 74 and 52 % for the native albumin and for component 1', respectively. The contents of β-structure were 19 and 23 % for the native albumin and for component 1', respectively. The wavelength of maximum intensity of tryptophan fluorescence shifted to lower wavelength, when the native albumin was changed to component 1'. This suggests that tryptophan residue(s) is transferred to a more hydrophobic environment.

The hydrogen ion titration curves, circular dichroism and fluorescence measurements, all supported the possibility that the component 2 is formed by the dimerization of component 1'. Further, it has been found that component 2' (dimer impurity in commercial bovine serum albumin preparations) is formed by the direct dimerization of native bovine serum albumin without conformational change.