Conformational changes in seventeen cystine disulfide bridges of bovine serum albumin proved by Raman spectroscopy.

Conformational changes in cystine disulfide bridges of bovine serum albumin during acid-induced isomerization (N --> F and F --> E transitions) have been studied with Raman spectroscopy. In an X-ray crystallographic study of human serum albumin, Carter and Ho reported that all disulfide bridges of the albumin molecule are in the gauche-gauche-gauche conformation [1]. On the other hand, the solution structure of bovine serum albumin examined by Raman spectroscopy differs from its crystal structure in the conformation of some of the disulfide bridges. Two Raman bands were detected at 520 and 505 cm(-1) in the disulfide stretching mode region, suggesting that the 17 disulfide bridges in the N-form of bovine serum albumin solution take both the gauche-gauche-gauche and gauche-gauche-trans conformations. The ratio of the peak intensities at 520 and 505 cm(-1) (I505/I520) is increased from 1.6 to 2.1 and from 2.1 to 6.3 on going from the N- to the F-form and from the F- to the E-form, respectively, indicating that the gauche-gauche-trans conformation of the disulfide bridges is converted to a gauche-gauche-gauche one which is the most energetically stable form during the acid-induced isomerization. However, small amounts of gauche-gauche-trans conformation still remain even in the E-form.