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.
Keywords: Rhodanese, ubiquitous, cyanide, detoxification, domain, thiosulphate, thiocyanate, mitochondrial enzyme, double
displacement mechanism, toluene, ageing, colonic epithelium, Rhodanese activity, rhodanese-selenium.
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