Thiocyanate formation, rhodanese

Table I. Thiocyanate formation from thiocystine and cyanide catalyzed by rhodanese .

Rhodanese domains I and 2 as an example of a protein with two domains that resemble each other extremely closely. Rhodanese is a liver enzyme that detoxifies cyanide by catalyzing the formation of thiocyanate from thiosulfate and cyanide. (Reprinted by permission of Jane S. Richardson.)... 

In the case of rhodanese, the rate of thiocyanate (SCN ) formation should be measured by usual chromogenic reactions for thiocyanate ions. 

Rhodanese provides an example of a thiol enzyme of a somewhat different type. This enzyme, which is widely distributed throughout nature, catalyses the formation of thiocyanate from thiosulphate and cyanide. This reaction probably does not represent the true biological... 

For release of HCN, the glucose is enzymically cleaved by linamari-nase and the cyanohydrin spontaneously decomposes (Figure 10.10). The cyanide once released can be detoxified as in plants, by conversion to cyanoalanine and asparagine (Figure 10.10), or by the enzyme rhoda-nese, which converts cyanide into the relatively innocuous thiocyanate. The formation and decomposition of HCN in millipedes and insects is therefore a remarkable example of parallel evolution, where insects and plants both produce HCN and benzaldehyde in similar ways and avoid the toxic eflfect of HCN by converting it to the same cyanoalanine. It is not easy to perform tests for the presence of rhodanese and so it is uncertain how widely it occurs in insects. 

Lang demonstrated that an enzyme which he called rhodanese (thiosulphate cyanide sulphurtransferase, E.C.-2.8.1.1.) accelerates the formation of thiocyanate from cyanide and thiosulphate, liver and kidney homogenates being p2irticularly active [41]. 

---