Oxygen-sensitive Reactions of Proteins and Peptides

In the previous paper (l), an oxygen-sensitive thermochromic system was described which involved reactions of anoxic liquid ammonia at 25” with peptides and proteins containing fully combined cystine. Few proteins are very soluble in liquid ammonia, and the question arose whether the reaction in such instances went to completion, the blue color produced representing the reaction product of all the fully combined cystine moieties present, or whether only a portion of such structures was responsible for the observed color. The behavior of reactive proteins in anoxic ammonia suggested investigating the effect of ammonia in the presence of oxygen. A further question naturally presented itself, namely the role of ammonia in the chromogenic reaction. Is ammonia unique or do other nitrogen-containing bases behave similarly? The experiments reported here were prompted by these questions.