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Methods of Protein Iodination
Published in Erwin Regoeczi, Iodine-Labeled Plasma Proteins, 2019
In general, HIO and its dissociation products are labile, more so in acidic and neutral than in alkaline solutions.20 However, above pH 10, they are again very unstable.10 The instability is due to the tendency to disproportionate according to Equation 7 in iodide and iodate at the ratio of 2:1. The cation seems to have some bearing on stability, for stability increases in the order of NalO <KIO < (NH4)IO.20 Pyridine also stabilizes aqueous hypoiodite. Disproportionation is not influenced by light, and it takes place more slowly in dilute solutions than in concentrated ones.
The skin’s endogenous antioxidant network
Published in Roger L. McMullen, Antioxidants and the Skin, 2018
Thus, for every two AscH− molecules depleted one is regenerated so that it may participate in further antioxidant protection. The other product of the disproportionation reaction is DHA, which is unstable and can rapidly decompose to other degradation products that interfere with enzymatic processes of the cell. Another fate of DHA is to be regenerated reductively to AscH− by the enzyme DHA reductase. The action of this enzyme is dependent on the available pool of GSH, as it is required as an electron donor.
Emulsion Rheology
Published in Laba Dennis, Rheological Proper ties of Cosmetics and Toiletries, 2017
Disproportionation is a result of the pressure inside a droplet being higher than the pressure outside the droplet. This driving force will create diffusion of chemical components from small droplets to larger ones or possibly into the continuous phase (Rieger, 1991). It may also result in small droplets becoming smaller and large droplets becoming larger, since different components of the surfactant system may diffuse from small to large droplets and vice versa at different rates.
Manganese dioxide nanosheets induce mitochondrial toxicity in fish gill epithelial cells
Published in Nanotoxicology, 2021
Cynthia L. Browning, Allen Green, Evan P. Gray, Robert Hurt, Agnes B. Kane
This route does not require any external electron donor because it is a disproportionation in which Mn(IV) is reduced while lattice oxygen, O, is oxidized to O2(g). These literature reports, together with the new data in this study, suggest that H+-mediated disproportionation of MnO2 nanosheets can occur at lysosomal pH values, even in the absence of biological antioxidants or other external electron donors. Although this biodissolution by disproportionation under mildly acidic conditions is slow (∼2 days) relative to the reductive route (∼minutes), it can occur over the time scales of in vitro cell experiments or particle clearance in vivo, and we thus propose this as a second distinct chemical pathway relevant for Mn2+ ion release in biological systems. In vivo, the combination of reducing agents, such as cysteine, and low pH in lysosomes makes it highly likely that MnO2 undergoes some dissolution within the lysosomal compartment, releasing Mn2+ ions.
Comparison of the antioxidant activities of nonfumigated and sulphur-fumigated Chrysanthemum morifolium cv. Hang-ju induced by oxidative stress
Published in Pharmaceutical Biology, 2021
Hongyan Ma, Shanshan Liu, Wenshan Qu, Qi Huang, Linyuan Li, Fujiang Chu, Yuyun Zhu, Xinlin Lv, Zhimin Wang, Jingjing Zhu
MDA is the aldehyde byproduct of ROS and indirectly reflects the degree of oxidative damage to the liver and endothelial cells. SOD is the only enzyme that employs oxygen free radicals as substrates in aerobic organisms. Thus, it is the most important enzyme in the body and can catalyse the disproportionation reaction of O2– to H2O2, which has a cytoprotective effect by blocking the production of toxic hydroxyl radicals. It has been reported that MDA increases SOD activity simultaneously decreases when lipid peroxidation is enhanced by serum lipid elevation (Niki 2010; Wang et al. 2017). Our results showed that SHJ decreased the activity of serum and cellular SOD and increased the contents of MDA and ROS, thereby enhancing lipid peroxidation, oxidative damage and membrane damage, which is unfavourable for the protection of metabolic functions in the body. This finding indicates that SF has a tremendous impact on the bioactivity and efficacy of HJ.
Phenylalanine 4-monooxygenase: the “sulfoxidation polymorphism”
Published in Xenobiotica, 2020
Stephen C. Mitchell, Glyn B. Steventon
Another fundamental problem is that the enzyme is generally regarded as a dioxygenase, attaching two oxygen atoms derived from molecular oxygen to form a sulfinic acid and not an unstable sulfenic acid. If it were to be involved in the metabolism of S-carboxymethyl-l-cysteine it would more likely produce a sulfone rather than a sulfoxide and trace amounts of the sulfone metabolite have only been reported once in human urine and may have been an artefact (Brockmoller et al., 1988). In general, compounds with a free sulfhydryl group are unable to form stable sulfenic acids, these compounds being transient intermediates that undergo disproportionation or self-condensation. To attain stability they require a polar or bulky grouping adjacent to the sulfenic acid moiety (Barrett, 1990; Hogg, 1990). With regards to cysteine, the sulfhydryl group needs to be substituted replacing the hydrogen atom with a more substantial moiety. S-carboxymethyl-l-cysteine is such a molecule with a carboxymethyl (–CH2COOH) entity being attached forming a thioether which may then produce a stable S-oxide. However, it is this addition to the cysteine molecule that presumably interferes with binding to the cysteine dioxygenase enzyme and moves the sulfur atom away from the catalytic site.