Pressure Jump Studies of Proteins. I. Isomerization of Bovine Serum Albumin at Neutral pH

Abstract

Pressure jump kinetic studies of the conformational change occurring in bovine serum albumin in neutral solutions have been carried out over the pH range 6.5–9.5. Two distinct relaxation effects are observed at each pH. The faster relaxation is attributed to binding of the dye to the protein, and the slower relaxation is related to the conformational change occurring in the protein. This slower relaxation effect is pH dependent with a maximum value near pH 8. Detailed analysis of these data leads to a mechanism for the conformational change which indicates that the one form of the protein has an ionizable group with a pK of 8.7 which changes to a pK of 6.7 when the protein undergoes the conformational change. A simple iterative procedure is given for analyzing the pH dependence of a relaxation time constant for a cyclic mechanism involving only one ionizing group controlling the conformational change.