Enzymes rhodanese

HCN is a systemic poison toxicity is due to inhibition of cytochrome oxidase, which prevents cellular utilization of oxygen. Inhibition of the terminal step of electron transport in cells of the brain results in loss of consciousness, respiratory arrest, and ultimately, death. Stimulation of the chemoreceptors of the carotid and aortic bodies produces a brief period of hyperpnea cardiac irregularities may also occur. The biochemical mechanisms of cyanide action are the same for all mammalian species. HCN is metabolized by the enzyme rhodanese which catalyzes the transfer of sulfur from thiosulfate to cyanide to yield the relatively nontoxic thiocyanate. 

HCN is detoxified to thiocyanate (SCN ) by the mitochondrial enzyme rhodanese rhodanese catalyzes the transfer of sulfur from thiosulfate to cyanide to yield thiocyanate, which is relatively nontoxic (Smith 1996). The rate of detoxification of HCN in humans is about 1 pg/kg/min (Schulz 1984) or 4.2 mg/h, which, the author states, is considerably slower than in small rodents. This information resulted from reports of the therapeutic use of sodium nitroprusside to control hypertension. Rhodanese is present in the liver and skeletal muscle of mammalian species as well as in the nasal epithelium. The mitochondria of the nasal and olfactory mucosa of the rat contain nearly seven times as much rhodanese as the liver (Dahl 1989). The enzyme rhodanese is present to a large excess in the human body relative to its substrates (Schulz 1984). This enzyme demonstrates zero-order kinetics, and the limiting factor in the detoxification of HCN is thiosulphate. However, other sulfur-containing substrates, such as cystine and cysteine, can also serve as sulfur donors. Other enzymes, such as 3-mercapto-pyruvate sulfur transferase, can convert... 

As noted in Section 4.4.1, the enzyme rhodanese is present to a large excess in the human body relative to its substrates, thus demonstrating zero... 

Dahl, A.R. 1989. The cyanide-metabolizing enzyme rhodanese in rat nasal respiratory and olfactory mucosa. Toxicol. Lett. 45 199-205. 

A factor of 3 was applied to the supporting studies as no specific susceptible populations were identified in monitoring studies or during the clinical use of nitroprusside solutions to control hypertension. The detoxifying enzyme rhodanese is present in all individuals including newborns. Application of the uncertainty factor to the El Ghawabi et al. (1975 as adjusted by the NRC) and Grabois (1954) data results in a value close to the 8-h 1 ppm concentration in the Leeser et al. (1990) study. 

No specific susceptible populations were identified during monitoring studies or during the clinical use of nitroprusside solutions to control hypertension. The detoxifying enzyme rhodanese is present in all individuals, including newborns. 

Cyanide is metabolized in the body by two metabolic pathways that have been identified (Ansell and Lewis 1970). The first and major metabolic pathway involves the transfer of sulfane sulfurs from a donor to cyanide to yield thiocyanate (see Section 2.3). The reaction employs the enzyme rhodanese as a... 

Exposure. Concentrations of cyanide and its metabolite thiocyanate can be measured in the blood, urine, and tissues. Since certain amounts of cyanide can always be found in the human tissues, urine, and expired air, only exposure to high doses can be detected by this way. Cyanide is metabolized in the body to thiocyanate in a reaction that is catalyzed by an enzyme rhodanese and mercaptopyruvate sulfur transferase (Ansell and Lewis 1970). 

Cyanide is readily detoxified in animals as all animal tissues contain the thiosulfate sulfurtransferase enzyme rhodanese. Rhodanese readily converts cyanide to the thiocyanate which is excreted in the urine. 

Lewis JL, Rhoades CE, Bice DE, et al. 1992. Interspecies comparison of cellular localization of the cyanide metabolizing enzyme rhodanese within olfactory mucosa. Anat Rec 232(4) 620-627. 

Cyanide has many sources natural (plant-Cassava), industrial (cyanide salts and nitriles), and accidental (fires). The target organ is the brain death is from respiratory arrest. Cyanide blocks cytochrome a-a3 (cytochrome oxidase) in mitochondria. The toxic level is 1 mg mL-1 in blood. Treatment involves giving dicobalt edetate (chelation). Alternatively, by giving NaNCb, levels of methemoglobin are increased, and this binds cyanide. Detoxication is catalyzed by the enzyme rhodanese, and this pathway may be increased by giving NaS207. 

Aminlari, M., Vaseghi, T., and Kargar, M. A., The cyanide-metabolizing enzyme rhodanese in different parts of the respiratory system in sheep and dogs, Toxicol. Appl. Pharmacol., 124, 64—71, 1994. 

Wood and Cooley, 1956). The mitochondrial enzyme rhodanese (thiosulfate sulfur transferase) is... 

Delayed ischaemic anoxia may also result from cyanide poisoning as a result of circulatory effects. There are several antidotal treatments, but the blood level of cyanide should be determined if possible as treatment may be hazardous in some cases. Cyanide is metabolized in the body, indeed up to 50% of the cyanide in the circulation may be metabolized in 1 h. This metabolic pathway involves the enzyme rhodanese and thiosulphate ion which produces thiocyanate (figure 7.461. However, the crucial part of the treatment is to reduce the level of cyanide in the blood as soon as possible and allow the cyanide to dissociate from the cytochrome oxidase. This is achieved by several means. Methaemoglobin will bind cyanide more avidly than cytochrome oxidase and therefore competes for the available cyanide. 

Another permanent cyanide detoxification method involves the intravenous injection of sodimn thiosulfate. The thiosulfate contains a loosely bound sulfur atom that can convert cyanide to thiocyanate by the action of the ubiquitous enzyme rhodanese (thiosulfate-cyanide sulfiutransferase). The much less toxic thiocyanate is excreted via the urine. Rhodanese occius in both the liver and in skeletal muscle and produces a detoxifying action even in the absence of thiosulfate. 

The third method involves using oxygen to supplement the second method, with the explanation that the enzyme rhodanese is not affected by oxygen. It should be added that artificial respiration with 100% oxygen should be instituted immediately if respiratory difficulty is observed (Rumack and Lovejoy, in Amdur et al., 1991, p. 933). 

The metabolic conversion of an isocyanide to an isothiocyanate had been inferred by studies on Ciocalypta sp. by Hagadone et al. [73]. Our own results showed that A. cavernosa may be capable of inserting sulphur onto an isocyanide metabolite. Alternatively the enzyme rhodanese, which is widespread in nature from sources such as bacteria, molluscs, and mammals [81, 82], or an equivalent enzyme irreversibly converts cyanide into thiocyanate prior to incorporation into the isothiocyanato group of (21). 

Atkinson et al. (1974) reported the antidote action of Kelocyanor [15137-09-4] and enzyme. The bacterial enzyme rhodanese [55073-14-8] mixed with sodium thiosulfate (40 xg and 100 mg/kg) was effective against NaCN in rabbits. Amyl nitrite is a common cyanide antidote. 

Both in vivo and, in water, in vitro, CS (o-chlorobenzylidene malononitrile) is hydrolyzed to 2-chlorobenzaldehyde and malononitrile. Malononitrile contains two cyanide moieties, and it is thought that at least one of these is liberated and attaches to sulfur via the enzyme rhodanese to form thiocyanate, which is excreted in the urine. 

The enzyme rhodanese (thiosulphate sulphurtran-sferase, EC.2.8.1.1) has a wide distribution among vertebrate tissues, and catalyses the conversion of cyanide into the less toxic thiocyanate ... 

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