The pH dependence of the reduced viscosity of modified serum albumins

Abstract

Viscosity measurements were carried out with bovine serum albumin (BSA), succinylated BSA, partially succinylated BSA, and methylated BSA, each being dissolved in aqueous solution containing 0.03 m KCl. The pH range covered was between 2.0 and 11.7. It was found that for BSA in aqueous solution, the reduced viscosity changes rapidly at pH below 4.3 and above 10.5, but remains constant at pH values between 4.3 and 10.5. For succinylated BSA and methylated BSA, the reduced viscosities show great changes in the pH region between 4.3 and 10.5. The changes of reduced viscosities for the two BSA derivatives, however, go in opposite directions. The reduced viscosity of partially succinylated BSA shows similarity to that of BSA in the pH region below 4.3 and above 10.5 and to succinylated BSA in the pH region between 4.3 and 10.5. The results demonstrate that the conformational change of the BSA molecule is a function of electrostatic charge. Models are discussed for BSA in neutral region and in acidic and basic regions respectively.