PubMed · 853984
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H J Holtmeier. 1977-04-22. [Hypervitaminoses].. https://pubmed.ncbi.nlm.nih.gov/853984/
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Ascorbic acid (AsA) is an essential nutritional component and powerful antioxidant in vegetables, and in plants, AsA levels are regulated by light. AsA levels in the leaves of Chinese chive (Allium tuberosum Rottler ex Spr), a popular vegetable, are poorly understood. Thus, this study was performed to assess the influence of light on AsA biosynthesis in chive and select related genes (AtuGGP1 and AtuGME1); in addition, bioinformatic analyses and gene expression level assays were performed. The biological information obtained for AtuGGP1 and AtuGME1 was analysed with several tools, including NCBI, DNAMAN, and MEGA11. After different light treatments were performed, the Chive AsA content and AtuGGP1 and AtuGME1 expression levels were determined. These results suggest that 1) compared with natural light, continuous darkness inhibited AsA synthesis in chives. 2) The amino acid sequences of AtuGGP1 and AtuGME1 are very similar to those of other plants. 3) The trends observed for the expression levels of AtuGGP1 and AtuGME1 were consistent with the AsA content observed in chives. Hence, we speculated that light controls AsA biosynthesis in chives by regulating AtuGGP1 and AtuGME1 expression. This study provided impactful and informative evidence regarding the functions of GGP and GME in chives.
An electron spin resonance (ESR) assay has been developed for peroxidase activity. The assay measures the formation of the paramagnetic nitroxide Tempol from the oxidation of its hydroxylamine derivative (TOLH) by short-lived radicals produced by peroxidase cycle intermediates, Compounds I and II. Using phenol as a peroxidase electron donor, the ESR approach is suitable for measurements of peroxidase activity ( > or = 0.003 U/ml) and micromolar quantities of H2O2 in sample sizes as small as 2 microliters. In addition, the ESR method can be used to continuously monitor activity in cell suspensions and other media that are susceptible to optical artifacts. The high membrane permeability of TOLH also makes it possible to estimate peroxidase activity in membrane-enclosed compartments, provided that TOLH oxidation rates can be stimulated with exogenous peroxidase reductants, e.g., phenol. Analysis of TOLH oxidation rates under conditions of low electron donor concentrations and high concentrations of H2O2 also shows clear indications of substrate-dependent inhibition and increased catalytic activity. Computer simulations indicate that the results obtained are consistent with the peroxidase reaction scheme proposed by Kohler et al. (1988, Arch. Biochem. Biophys. 264, 438-449) modified to correct for a nitroxide dependent stimulation of peroxidase catalytic activity.
Effects of ethanol (EtOH), mannitol (Man), L-histidine (His) and glutathione (GSH) on the oxidation of 2'-deoxyguanosine (dG) to its 8-hydroxy derivative (8-OH-dG) with H2O2 plus L-ascorbic acid (Ascb) in the absence and presence of Ni(II) were investigated in order to unveil the nature of active oxygen species involved in that oxidation. In the absence of Ni(II), production of 8-OH-dG was inhibited by His much greater than GSH greater than or equal to GSSG (oxidized glutathione) much greater than EtOH, but not by Man. The latter tended to enhance the production of 8-OH-dG. In the presence of Ni(II), the inhibition by His, GSH and GSSG, but not EtOH, was prevented. The results indicate involvement of a 'crypto-hydroxyl' radical as the dG oxidizing species in both the absence and presence of Ni(II). Also, the results provide evidence that Ni(II) complexes with His, GSH and GSSG may lack antioxidant capacity. Moreover, the Ni(II) complex with His was found capable of enhancing 8-OH-dG production by the Ascb+H2O2 system to a greater extent than Ni(II) alone. Likewise, although to a lesser extent, the formation of 8-OH-dG was enhanced by the combination of Ni(II) and Man which do not form complexes at pH 7.4. Since His is a major Ni(II) carrier in animal tissues, the dG oxidation enhancing capacity of the Ni(II) complex with His may contribute to the toxic and carcinogenic effects of Ni(II).