Salt Linkages in Proteins

Abstract

THE original conception of Speakman^1-3 that salt linkages are important structural elements in micelles of fibrous proteins like keratin has been extended more recently^4,5 to include molecules of globular proteins in aqueous solution. Although there is some vagdeness with respect to the exact physical character of the linkages in question, their hypo-thetical properties as outlined by Eyring and Stearn⁵ seem to classify them as hydrogen bonds between the ionizable amino and carboxylic groups of the side-chains of amino-acids (Mirsky and Pauling⁴). In such bonds the close approach of the opposite charges makes them appear as essentially neutral to the surroundings, and their instability in the presence of water requires that they are in protected positions inside the protein molecule⁴. Still, they are supposed to react with protons, and in Eyring and Steam's theory⁵, therefore, any protolytic reaction of a dissolved protein involves the breaking or formation of hydrogen bonds between carboxylic and amino groups. Since these bonds are regarded as characteristic of native proteins as distinct from denatured ones^4,5, there is supposed to be an element of denaturation and renaturation in all protolytic reactions.