The Physical Chemistry of the Proteins in Non-aqueous and Mixed Solvents.* I. the State of Aggregation of Certain Proteins

The use of solvents, other than water, that are capable of dissolving proteins without entering into chemical combination with them, in contrast to the usual mode of procedure, by the addition of small amounts of acid or alkali, makes it possible to investigate the properties of proteins in one of their most important states, the isoelectric state. In the present investigation, one such property, the osmotic pressure, was measured chiefly, with the use of ureawater mixtures as a solvent. The main objectives in mind were: (1) to develop a method for the determination of molecular weights of proteins that are not soluble in water in the isoelectric state, and (2) to determine whether proteins are capable of undergoing changes in their state of aggregation with changes of solvent. Neutral solvents other than water have been little used in connection with protein studies. Cooper and Nicholas (1) find that, in general, proteins are insoluble in organic solvents. It has long been known that mixtures of alcohol and water dissolve a class of proteins known as the prolamines, which do not dissolve in either of the pure components. This mixed solvent is, however, specific for the prolamines. A few-organic solvents are known to bring into solution, without entering into chemical combination, some of the most insoluble proteins. Urea, for example, when dissolved in a small amount of water has a powerful solvent action on many proteins, irrespective of their class. Besides urea solu-