Cyanide is an important industrial chemical produced on a grand scale each year. Although extremely toxic to mammalian life, cyanide is a natural product generated by fungi and bacteria, and as a result microbial systems have evolved for the degradation of cyanide to less toxic compounds. The enzymes which utilize cyanide as a substrate can be categorized into the following reaction types: substitution/addition, hydrolysis, oxidation, and reduction. Each of these categories is reviewed with respect to the known biochemistry and feasibility for use in treatment of cyanide containing wastes.

Microbes and microbial enzymes for cyanide degradation.

A gene encoding rhodanese (rhdA) was cloned from Azotobacter vinelandii on a 2.3-kb SphI fragment. This fragment was identified by its hybridization to a PCR product obtained by amplification of genomic DNA using degenerate primers encoding the N-terminal sequence of rhodanese purified from A. vinelandii. The sequence of a 1.2-kb region revealed an 813-bp open reading frame that encoded a polypeptide of 271 amino acids, the N-terminal sequence of which was identical to that of A. vinelandii rhodanese. In a search of database entries, eukaryotic rhodaneses and rhodanese-like proteins from bacteria gave the highest scores of identity (27–30%) with the predicted product of the 813-bp open reading frame. A. vinelandii RhdA shows less sequence similarity to vertebrate rhodaneses than it does to prokaryotic rhodanese-like proteins which did not show typical rhodanese activity. Basic residues thought to be catalytically important in bovine rhodanese are not conserved in A. vinelandii rhodanese. The sequence similarity between the two structurally similar domains of rhodanese is more pronounced for the A. vinelandii enzyme than the bovine enzyme, and supports the hypothesis that the complete structure was originally generated by gene duplication. When rhdA was overexpressed in Escherichia coli, rhodanese represented 30% of total cell protein and thiosulfate:cyanide sulfurtransferase activity increased >600 fold in cell-free extracts. A. vinelandii rhdA insertion/deletion mutants had no discernible phenotype distinct from the wild-type strain with respect to growth on various sulfur sources or nitrogenase activity. Mutants retained 20% of wild-type rhodanese thiosulfate: cyanide sulfurtransferase activity suggesting the presence of redundant sulfurtransferase enzymes in A. vinelandii.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1996.00240.x

Cloning, Sequence Analysis and Overexpression of the Rhodanese Gene of Azotobacter vinelandii

Sodium 2-propenyl thiosulfate, a water-soluble organo-sulfane sulfur compound isolated from garlic, induces apoptosis in a number of cancer cells The molecular mechanism of action of sodium 2-propenyl thiosulfate has not been completely clarified In this work we investigated, by in vivo and in vitro experiments, the effects of this compound on the expression and activity of rhodanese Rhodanese is a protein belonging to a family of enzymes widely present in all phyla and reputed to play a number of distinct biological roles, such as cyanide detoxification, regeneration of iron–sulfur clusters and metabolism of sulfur sulfane compounds The cytotoxic effects of sodium 2-propenyl thiosulfate on HuT 78 cells were evaluated by flow cytometry and DNA fragmentation and by monitoring the progressive formation of mobile lipids by NMR spectroscopy Sodium 2-propenyl thiosulfate was also found to induce inhibition of the sulfurtransferase activity in tumor cells Interestingly, in vitro experiments using fluorescence spectroscopy, kinetic studies and MS analysis showed that sodium 2-propenyl thiosulfate was able to bind the sulfur-free form of the rhodanese, inhibiting its thiosulfate:cyanide-sulfurtransferase activity by thiolation of the catalytic cysteine The activity of the enzyme was restored by thioredoxin in a concentration-dependent and time-dependent manner Our results suggest an important involvement of the essential thioredoxin–thioredoxin reductase system in cancer cell cytotoxicity by organo-sulfane sulfur compounds and highlight the correlation between apoptosis induced by these compounds and the damage to the mitochondrial enzymes involved in the repair of the Fe–S cluster and in the detoxification system

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1742-4658.2008.06535.x

Rhodanese-thioredoxin system and allyl sulfur compounds.

Natural allyl sulfur compounds show antiproliferative effects on tumor cells, but the biochemical mechanisms underlying the antitumorigenic properties of the organ sulfur compounds are not yet fully understood Sodium 2-propenyl-thiosulfate is a garlic water-soluble organo-sulfane sulfur compound able to promote apoptosis in cancer cells, affecting the 'managing' of the redox state in the cell Our studies show that sodium 2-propenyl-thiosulfate reacts spontaneously with reduced glutathione at physiological pH, leading to the formation of S-allyl-mercapto-glutathione, radicals and peroxyl species, which are able to induce inhibition of enzymes with cysteine in the catalytic site, such as sulfurtransferases S-Allyl-mercapto-glutathione was purified and characterized by NMR and MS, and its cytotoxic effect at 500 μm on HuT 78 cells was analyzed, showing activation of the p38-MAPK pathway Many allyl sulfur compounds are also able to promote chemoprevention by induction of xenobiotic-metabolizing enzymes, inducing down-activation or detoxification of the carcinogens Thus, the effects of the S-allyl-mercapto-glutathione on proteins involved in the cellular detoxification system, such as glutathione S-transferase, have been evaluated both in vitro and in HuT 78 cells Although the antitumor properties of water-soluble sulfur compounds may arise from several mechanisms and it is likely that more cellular events occur simultaneously, a relevant role is played by the formation of both reduced glutathione conjugates and radical species that affect the activity of the thiol-proteins involved in fundamental cellular processes

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1742-4658.2011.08407.x

Oxidative species and S-glutathionyl conjugates in the apoptosis induction by allyl thiosulfate

Active site reactivity and specificity of RhdA, a thiosulfate:cyanide sulfurtransferase (rhodanese) from Azotobacter vinelandii, have been investigated through ligand binding, site-directed mutagenesis, and X-ray crystallographic techniques, in a combined approach. In native RhdA the active site Cys230 is found persulfurated; fluorescence and sulfurtransferase activity measurements show that phosphate anions interact with Cys230 persulfide sulfur atom and modulate activity. Crystallographic analyses confirm that phosphate and hypophosphite anions react with native RhdA, removing the persulfide sulfur atom from the active site pocket. Considering that RhdA and the catalytic subunit of Cdc25 phosphatases share a common three-dimensional fold as well as active site Cys (catalytic) and Arg residues, two RhdA mutants carrying a single amino acid insertion at the active site loop were designed and their phosphatase activity tested. The crystallographic and functional results reported here show that specific sulfurtransferase or phosphatase activities are strictly related to precise tailoring of the catalytic loop structure in RhdA and Cdc25 phosphatase, respectively.

A persulfurated cysteine promotes active site reactivity in Azotobacter vinelandii Rhodanese.

Identification of sulfurtransferase enzymes in Azotobacter vinelandii.

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Identification of sulfurtransferase enzymes in Azotobacter vinelandii.