Intramolecular sulfhydryl‐catalyzed structural alteration of bovine plasma albumin–N‐A isomerization*

The N‐A isomerization of bovine plasma albumin (BPA) (the intramolecular sulfhydryl‐disulfide exchange reaction) is not a two‐state but a multi‐state reaction as shown in the following equation N ± A1 + mH+ ± A2 + nH+ ± where N and A1 are the N‐ and A(aged)‐forms, respectively. The N‐A isomerization was strongly suppressed by increasing the ionic strength, especially by divalent cations, such as Ca2+. The N‐A isomerization was completely suppressed in the presence of 20 mM sodium caprylate and 40 mM N‐acetyltryptophan. This suppression of the intramolecular sulfhydryl‐disulfide exchange reaction might be due to the reduction of the structural fluctuation of BPA.