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Glutathione, Cysteine, and the Neuromelanin Pathway : Potential Roles in the Pathogenesis of Parkinson’s Disease—a New Hypothesis
Published in Christopher A. Shaw, Glutathione in the Nervous System, 2018
Furthermore, it is becoming increasingly evident that genetic factors might also play important roles in the susceptibility to PD (Golbe et al. 1990; Johnson, Hodge, and Duvoisin 1990). It is conceivable that these genetic factors might be linked to the observations that an extraordinarily high percentage of PD patients have very low activities of cysteine dioxygenase (Steventon et al. 1989) and thiolmethyl transferase (Waring et al. 1989). These are peripheral enzymes that play key roles in the detoxification and elimination of environmental toxicants and xenobiotics. Thus, it has been suggested that chronic exposure of individuals genetically equipped with these defective enzyme systems to certain environmental toxicants might permit some of these substances to cross the blood–brain barrier (BBB), enter the brain, and contribute to the degeneration of nigrostriatal DA neurons and PD (Steventon et al. 1989; Waring et al. 1989). However, no agricultural or industrial toxicant has been identified in the environment that can act as a selective nigrostriatal dopaminergic neurotoxin and cause PD.
Research on the hepatotoxicity mechanism of citrate-modified silver nanoparticles based on metabolomics and proteomics
Published in Nanotoxicology, 2018
Jiabin Xie, Wenying Dong, Rui Liu, Yuming Wang, Yubo Li
Cysteine catabolism mainly proceeds the oxidation of cysteine sulfate. In the cysteine dioxygenase (CDO) catalytic reaction, dioxyl is added to cysteine to form a cysteine sulfinic acid, which is further converted to alanine (Ueki et al. 2011). Alanine enters the liver through the blood, combining with deamination and releasing ammonia to synthesize urea, which is an important biological function of liver cells. Since AgNP-cit decreases the alanine content, urea synthesis is obstructed in the liver, causing liver damage (Su et al. 2017). Meanwhile, the methionine content was significantly reduced in the cysteine and methionine metabolic pathways, suggesting that cysteine and methionine metabolism was abnormal and that the liver was seriously injured by the effects of AgNP-cit (Dominy, Hwang, and Stipanuk 2007). AgNP-cit up-regulated L-serine dehydratase/L-threonine deaminase and phosphoglycerate mutase, and down-regulated cysteine dioxygenase, alanine, isoleucine and methionine in the liver, which are involved in oxidation, and deamination. This led to abnormalities of glycine, serine and threonine metabolism, cysteine, and methionine metabolism, thus resulting in liver damage.
Xenobiotic C-sulfonate derivatives; metabolites or metabonates?
Published in Xenobiotica, 2018
The oxygenation of cysteine to cysteine sulfinic acid via cysteine dioxygenase (EC 1.13.11.20), subsequent decarboxylation to hypotaurine via sulfoalanine decarboxylase (EC 4.1.1.29) and oxidation via hypotaurine dehydrogenase (EC 1.8.1.3) yields taurine (2-aminosulfonic acid), an ubiquitous molecule in animals (Huxtable, 1992; Jacobsen & Smith, 1968). However, all of the enzymes involved in this synthesis sequence are finely tuned to their role in intermediary metabolism and their substrate specificities are extremely narrow. This is correct also for side-reactions and parallel anabolic routes. It is doubtful that a molecule differing much from their natural substrates would be able to be metabolized by these enzymes.
Phenylalanine 4-monooxygenase: the “sulfoxidation polymorphism”
Published in Xenobiotica, 2020
Stephen C. Mitchell, Glyn B. Steventon
Despite prolonged investigation, no other substrates for cysteine dioxygenase (CDO, l-cysteine: oxygen oxidoreductase, E.C. 1.13.11.20) have been reported as its function appears specific to its role in the conversion of l-cysteine to cysteine sulfinic acid (3-sulfino-l-alanine; 2-amino-3-sulfinopropionic acid). However, bacterial analogues of the enzyme do show some substrate variance, being able to oxidise closely related compounds such as 3-mercaptopropionate (l-cysteine minus the amino grouping) to produce 3-sulfinopropionate (Bruland et al., 2009; Wenning et al., 2016) but will not metabolise homocysteine, N-acetylcysteine or cysteamine (Tchesnokov et al., 2015).