Reactions of cyanamide with methaemoglobin and some other haematin compounds

Cyanamide reacts with methaemoglobin to give a red compound with a characteristic absorption spectrum. Cyanamide also combines with whale metmyoglobin and Tubifex methaemoglobin. These compounds are best formed in alkaline solution, one molecule of cyanamide combining per atom of haematin iron. Cyanamide acts as an inhibitor of the cytochrome oxidase system but is 300 times less effective than cyanide or azide. Contrary to certain claims, no compound formation was observed between cyanamide and free haematins, haems or their derivatives. The significance of these results and the possible mode of combination of cyanamide with methaemoglobin are discussed in the light of the effects of KCN, methyl isocyanide and acetonitrile on haemoproteins and free haematins.