The Denaturation and Hydration of Proteins. I*

Of the different kinds of denaturation of proteins, that by heat has been investigated most thoroughly. The theory has been put forward that the loss of the zwitter ion structure by an interaation of the ionogenic groups is the most important of the electrochemical changes which a protein undergoes by the action of heat (Pauli (6), Cohn (2)). The question as to whether other structural changes are brought about by heat denaturation has been discussed by many investigators (Pauli, Haurowita. Wu, cited in (7)) but is still unsettled at the present time. In a recent paper, Mirsky and Anson (3) presented evidence that certain groups become detectable when a protein is denatured (-SH and -S-Sgroups), whereas they are undetectable in the natural state. Little attention has been paid to the denaturation of proteins at an air-water interface. In a recent paper the theory has been advanced that this kind of denaturation, the surface denaturation, is closely related to the formation of surface films (Neurath (4)). Both processes involve an unfolding of the peptide chains which in the natural state are curled up in the interior of the molecule and become stretched out when the molecule comes in contact with the surface of the bulk solution. This kind of denaturation is probably important biologically because it occurs by mere shaking of a protein solution, to some extent even spontaneously. In this paper we have investigated the differences between the denaturation by heat and by surface forces. The affinity of a substance for the solvent is likewise an important characteristic of its structure and is conditioned by the lyo-