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.