The Reactions of Formaldehyde with Amino Acids and Proteins

Abstract

Publisher Summary This chapter focuses on the reactions of formaldehyde with amino acids and proteins. Formaldehyde is a reagent familiar to all protein chemists through its employment in the formol titration of amino acids and peptides. Formaldehyde has been widely used as a tanning agent for collagen and other fibrous proteins. Like other such agents, it renders these proteins relatively inert to digestion with trypsin and greatly decreases their tendency to swell in water or in acid or alkaline solutions. All these properties of formaldehyde are of great interest, both theoretically and practically. Formaldehyde can combine with any one of a number of different kinds of functional groups found in proteins. When steric relations are favorable, it can react with two such groups, forming a methylene bridge between them. It is reactions of the latter type that are most likely to modify the mechanical properties of the protein. Thus, the interpretation of observed changes in the properties of the proteins is rendered extremely difficult by the multiplicity of possible reactions that must be considered. The remarkable variety of these reactions has not always been fully realized by those who have employed formaldehyde as a reagent. Some of the reactions are rapid, some are slow; some are readily reversible, some practically irreversible; some proceed readily even at room temperature, and others only at higher temperatures. Their nature is far more easily discerned when only one or two functional groups are involved, as in the amino acids and dipeptides, rather than in the more complex peptides and the proteins.