The E F F E C T of Denaturation on the Viscosity of Protein Systems by M. L. Anson A~d

Concentrated solutions of proteins in acid or alkali may become very viscous on denaturation of the protein and under suitable conditions a moderately viscous solution can be converted by heating into a clear gel. These striking changes in viscosity, although they have been known for a long time, have not been studied in detail in recent years and in general the study of denaturation has been neglected. The main reason for this neglect has been the belief that denaturation is an irreversible reaction, probably an irreversible splitting up of the protein, and that therefore denaturation is of little physiological interest. The experiments described in previous papers (reviewed in Anson and Mirsky, 1931a) led us to the conclusion that the denaturation and coagulation of proteins, contrary to the usual notion, are reversible; and that therefore denaturation is a biologically possible process. We accordingly became interested in resuming the older investigations of the gross change in viscosity accompanying denaturation. The present experiments make more precise than was possible a generation ago the conditions for obtaining very viscous solutions and gels, and they show that one can convert not only a concentrated protein solution but even a solution containing only one per cent of protein into a clear gel. Although, as will be seen, there is an increase in viscosity due to denaturation itself apart from any aggregation of the molecules, in the very viscous solutions containing little protein the denatured protein seems to be in the form of aggregates, invisible precipitates, which occlude water.