A proportion of the plant's l-ascorbate (vitamin C) occurs in the apoplast, where it and its metabolites may act as pro-oxidants and anti-oxidants. One ascorbate metabolite is 2,3-diketogulonate (DKG), preparations of which can non-enzymically generate H2O2 and delay peroxidase action on aromatic substrates. As DKG itself generates several by-products, we characterised these and their ability t...

Glycolate oxidase that was partially purified from pea leaves was inactivated in vitro by blue light in the presence of FMN. Inactivation was greatly retarded in the absence of O2. Under aerobic conditions H2O2 was formed. The presence of catalase, GSH or dithiothreitol protected glycolate oxidase against photoinactivation. Less efficient protection was provided by ascorbate, histidine, tryptop...

High light stress decreases the photosynthetic rate in plants due to photooxidative damage apparatus, photoinhibition of PSII, and/or PSI. The dissipation excess energy by nonphotochemical quenching and degradation D1 protein PSII its repair cycle help against damage. Light also activates stress-responsive nuclear genes through accumulation phosphonucleotide-3'-phosphoadenosine- 5'-phosphate, m...

showed no respiration due to endogenous substrates. Only L-ascorbate with NNN‘N’tetramethyl-p-phenylenediamine was oxidized by membrane particles and the specific activity obtained was lower than in corresponding particles prepared from NH4+-grown cells. Low-temperature reduced-minus-oxidized difference spectra (Fig. 1, trace b) suggested that this lack of electron-transport activity may be due...

Though there are undoubtedly multiple functions for glutathione yet to be appreciated we do know that glutathione is: • a co-factor for the glutathione peroxidases, which are crucial selenium-containing antioxidant enzymes. • a co-factor for glutathione S-transferases, enzymes which are involved in the detoxification of xenobiotics, including carcinogens. • involved in the regeneration of ascor...

Recycling of ascorbic acid from its oxidized forms is required to maintain intracellular stores of the vitamin in most cells. Since the ubiquitous selenoenzyme thioredoxin reductase can recycle dehydroascorbic acid to ascorbate, we investigated the possibility that the enzyme can also reduce the one-electron-oxidized ascorbyl free radical to ascorbate. Purified rat liver thioredoxin reductase c...

Low millimolar concentrations of ascorbate are capable of inflicting lethal damage on a high proportion of cancer cells lines, yet leave non-transformed cell lines unscathed. Extracellular generation of hydrogen peroxide, reflecting reduction of molecular oxygen by ascorbate, has been shown to mediate this effect. Although some cancer cell lines express low catalase activity, this cannot fully ...

Substrate kinetic properties of cytochrome oxidase in rat liver, kidney, brain and heart mitochondria were examined using ascorbate + N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) as the electron donor system. Analysis of the substrate kinetics data revealed tissue-specific expression of kinetic components exhibiting differences with respect to Km, Vmax and Kcat/Km values. Regression analysis...