The Action of Alkalies

In a previous communication I we reported on the action of weak and of stronger alkali on dextro-alanyl-dextro-alanine anhydride. I t was observed that the anhydride was partially racemized if it was allowed to remain in an aqueous solution containing one equivalent of sodium hydroxide for 24 hours. When the concentration of the alkali was increased tenfold, the anhydride was rapidly converted into the dipeptide and the latter preserved its normal optical activity in the course of 72 hours. I t was then suggested that, if found to be general, this peculiarity could have a theoretical and a practical value: first, it could be used for the detection of the presence of ketopiperazines in the protein molecule; secondly, it might furnish an explanation as to the mechanism of the racemization of proteins. Dakin was the first to advance a comprehensive theory of this phenomenon in protein. Kossel and Weiss prior to Dakin observed that when proteins are acted upon by half normal alkalies, certain of their component amino acids lose part or all of their optical activity, whereas other amino acids remain with their optical activity unimpaired. Dakin sought to explain this phenomenon by the assumption that only those amino acids are racemized which are situated between two other amino acids. Thus, in a tripeptide, only the central and not the terminal amino acids can be racemized. Dakin further postulated that the intermediate phase in the process of racemization consisted in an enolic tautomerization. Thus, considering the case of glycyl-levo-