Cyanide Detoxifying Enzyme: Rhodanese

Rhodanese is an ubiquitous enzyme active in all living organisms from bacteria to man. It is multifunctional enzyme but plays central role in cyanide detoxification. This enzyme is also widely distributed in plants. It functions through double displacement (ping pong) mechanism. The activity of rhodanese in a particular tissue reflect the ability of that tissue to detoxify cyanide. The level of rhodanese in different tissues of animals is correlated with the level of exposure to cyanide. Mitochondrial bovine rhodanese is the best characterized rhodanese which is 293 amino acids long consisting of inactive N-terminal and catalytic C-terminal domain. It comprises of single polypeptide chain of 32,900 Da folded into two domains of about equal size. Active site of rhodanese has essential sulfhydryl and aromatic groups in close proximity. In addition to this, competitive inhibition of rhodanese by aromatic ions suggests the presence of tryptophanyl residue at the active center. Sequence analysis of rhodanese-like proteins highlights their heterogeneity to form rhodanese superfamily presenting variably arranged rhodanese domains as single or tandem domains, or combined with other protein domains. Many methods for rhodanese assay have been reported but the most common one is colorimetric estimation of thiocyanate formed from the reaction of cyanide with thiosulphate catalyzed by rhodanese.