13] Pressure effects in ultracentrifugation of interacting systems

Abstract

Publisher Summary This chapter discusses the effect of the pressure gradient developed in high and low speed centrifugation on the distribution of species in the chemically reacting systems of macromolecules. The current theories of sedimentation equilibrium of interacting systems do not in general take into account the possibility of changes in the partial specific volume on association, and no theory exists for the effect of these changes on transport processes in velocity sedimentation experiments. As pressures of the order of 100–500 atm are generated at the base of a centrifuge cell at high rotor speeds, even extremely small changes in specific volume can lead to marked effects in sedimentation behavior. Over the past few years, a number of well-documented studies demonstrating volume changes on polymerization of proteins have been reported. In general, these aggregation reactions show positive volume increments, in the absence of denaturing conditions, suggesting that ionic or hydrophobic bonding plays a dominant role in the polymerization process. The evidence is strong that the formation of such bonds in aqueous systems requires a decrease in ordered water structure about the groups involved in bonding leading to a positive volume change of about 10–20 cc/mole bond.