Enzymatic conversion of cyanide to thiocyanate.

T HE minute amounts of thiocyanate normally present in urine, blood and saliva have stimulated the interest of many workers as to the origin of the cyanide and the pattern of conversion of cyanide to thiocyanate. The problem has toxicologic as well as physiologic importance because of the great toxicity of cyanide. The detoxication of cyanide in the animal body was first demonstrated by S. Lang (I, 2) who was able to show that after the injection of cyanide or of aliphatic nitriles in the rabbit, an increased amount of thiocyanate was excreted in the urine. Similar findings were reported by Heymanns and Mesoin (3). The formation of minute amounts of cyanide from products of protein metabolism and from the nitriles ordinarily present in foods and the conversion of that cyanide to thiocyanate was believed by these authors to account for the thiocyanate normally excreted from the body. The in vitro studies of this mechanism were initiated by Pascheles (4), who showed that liver and muscle tissue from the dog were able to produce thiocyanate after digestion with sodium cyanide, liver being more active in this respect than muscle. Kahn (5) concluded from this work and from a series of liver perfusion experiments in which the amount of thioctinate produced increased with the number of perfusion trips that the liver was an active factor in the production of thiocyanate. In 1933 Konrad Lang (6, 7) reported his experiments on the iut vitro production of thiocyanate from cyanide in the presence of sulfur. He postulated that an enzyme was responsible for the conversion of cyanide to thiocyanate, described it as heatlabile and rapidly acting, and gave PH and substrate-concentration optima. The enzyme, which he termed ‘rhodanese,’ was widely distributed in animal tissues and was present in large amounts in the liver. Lang, therefore, suggested that the formation of thiocyanate was the principal route of detoxication of cyanide in the body and that the liver was the chief site of this detoxication. Cosby and Sumner (8) puri-fied this enzyme to some extent and made further studies of its properties. This paper deals largely with the distribution of the enzyme in various organs and tissues.