CD‐resolved secondary structure of bovine plasma albumin in acid‐induced isomerization*

Abstract

Bovine plasma albumin (BPA) showed the acid-induced two-step transition, the N-F transition and acid-expansion. Changes in fractions of α-helix (f_α), β-form (f_β) and unordered form (f_R) in the acid-induced isomerization of BPA were studied using the method of Chen et al. (1972) with two constraints: f_i = 1, 0 ± f_i ± 1. pH-profiles of f_α and f_R showed the two-step change, one corresponding to the N-F transition and the other to the acid-expansion in 0.10 m KCl and in 0.02 m NaClO₄. pH-profile of f_β showed one-step change, correlating to the later part (lower pH side) of the N-F transition. The N-F transition might thus involve the helix ± β and helix ± coil transitions.