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Glutamine and its Neuroactive Derivatives in the Retina
Published in Elling Kvamme, Glutamine and Glutamate in Mammals, 1988
In summary, and based on current premises, there is convincing evidence that some photoreceptors use glutamate or aspartate as their neurotransmitter. However, it should be noted that photoreceptors contain high levels of the sulfonic amino acid taurine39,40 and there is the suggestion that this also may have differential effects on “off” and “on” bipolar cells.39 More recently, immunohistochemical staining for cysteine sulfinic acid decarboxylase (CSAD), a key enzyme in the synthesis of taurine from cysteine, has shown it to be present in the synaptic vesicles of some rod and cone photoreceptors of the rat retina,41 and cysteine is readily taken up and metabolized by photoreceptor cells.40 Moreover, there is evidence to suggest that cAAT and cysteine sulfinic acid aminotransferase have co-identity.42-43 Thus, transmitter roles for taurine and its neuroactive relatives cysteine sulfinic and cysteic acids cannot be excluded; more comparative studies are needed.
Taurine enhances mouse cochlear neural stem cells proliferation and differentiation to sprial gangli through activating sonic hedgehog signaling pathway
Published in Organogenesis, 2018
Xinghua Huang, Weijing Wu, Peng Hu, Qin Wang
Taurine is the most abundant and widely distributed amino acid in human tissues with fundamental physiological functions.1 The endogenous taurine is mainly synthesized in pancreas via the cysteine sulfinic acid pathway,2 while exogenous source can be obtained from regular diet including egg, meat and seafood.3 It’s been disclosed that relatively high concentration of intrinsic taurine localizes in the heart and retina, which underlies its essential roles in cardiovascular function, development and function of skeletal muscle, retina and the central nervous system.4 Accumulative evidences indicated the protective effects on neural system of supplemented taurine. For example, the intracerebral taurine concentration was significantly induced in the neurons impaired by hypoxia-ischemia in rodents.5 Transient deprivation of oxygen and glucose impaired the neural progenitor cell differentiation into functional neurons, which was ameliorated by taurine treatment. Taurine simultaneously improved cell viability and proliferation of the neural progenitor cells.6 In addition, taurine in vitro administration was shown to promote the proliferative index of neural progenitor cells isolated from mouse embryonic mesencephalon, dentate gyrus and human embryonic brain.7–9 In line with these neural protective effects, our previous study demonstrated that taurine treatment significantly stimulated proliferation, differentiation and neurite outgrowth of cochlea neural stem cells (NSCs).10 However, the molecular mechanism underlying this phenotype is yet to be elucidated.
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).