Oxidative decarboxylation of glycollate and glyoxylate by leaf peroxisomes.
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ABSTRACT:
SUBMITTER: Halliwell B
PROVIDER: S-EPMC1166198 | biostudies-other | 1974 Feb
REPOSITORIES: biostudies-other
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Project description:Doxorubicin, a commonly used anti-neoplastic agent, causes severe neurotoxicity. Doxorubicin promotes thinning of the brain cortex and accelerates brain aging, leading to cognitive impairment. Oxidative stress induced by doxorubicin contributes to cellular damage. In addition to mitochondria, peroxisomes also generate reactive oxygen species (ROS) and promote cell senescence. Here, we investigated if doxorubicin affects peroxisomal homeostasis in neurons. We demonstrate that the number of peroxisomes is increased in doxorubicin-treated neurons and in the brains of mice which underwent doxorubicin-based chemotherapy. Pexophagy, the specific autophagy of peroxisomes, is downregulated in neurons, and peroxisomes produce more ROS. 2-hydroxypropyl-β-cyclodextrin (HPβCD), an activator of the transcription factor TFEB, which regulates expression of genes involved in autophagy and lysosome function, mitigates damage of pexophagy and decreases ROS production induced by doxorubicin. We conclude that peroxisome-associated oxidative stress induced by doxorubicin may contribute to neurotoxicity, cognitive dysfunction, and accelerated brain aging in cancer patients and survivors. Peroxisomes might be a valuable new target for mitigating neuronal damage caused by chemotherapy drugs and for slowing down brain aging in general.
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Project description:Peroxisomes, single-membrane-bounded organelles with essentially oxidative metabolism, are key in plant responses to abiotic and biotic stresses. Recently, the presence of nitric oxide (NO) described in peroxisomes opened the possibility of new cellular functions, as NO regulates diverse biological processes by directly modifying proteins. However, this mechanism has not yet been analysed in peroxisomes. This study assessed the presence of S-nitrosylation in pea-leaf peroxisomes, purified S-nitrosylated peroxisome proteins by immunoprecipitation, and identified the purified proteins by two different mass-spectrometry techniques (matrix-assisted laser desorption/ionization tandem time-of-flight and two-dimensional nano-liquid chromatography coupled to ion-trap tandem mass spectrometry). Six peroxisomal proteins were identified as putative targets of S-nitrosylation involved in photorespiration, ?-oxidation, and reactive oxygen species detoxification. The activity of three of these proteins (catalase, glycolate oxidase, and malate dehydrogenase) is inhibited by NO donors. NO metabolism/S-nitrosylation and peroxisomes were analysed under two different types of abiotic stress, i.e. cadmium and 2,4-dichlorophenoxy acetic acid (2,4-D). Both types of stress reduced NO production in pea plants, and an increase in S-nitrosylation was observed in pea extracts under 2,4-D treatment while no total changes were observed in peroxisomes. However, the S-nitrosylation levels of catalase and glycolate oxidase changed under cadmium and 2,4-D treatments, suggesting that this post-translational modification could be involved in the regulation of H(2)O(2) level under abiotic stress.
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Project description:1. An enzyme system that catalyses a synergistic decarboxylation of glyoxylate and 2-oxoglutarate has been purified from pig-liver mitochondria. 2. The purified system is specific for glyoxylate and 2-oxoglutarate as substrates, although in earlier stages of purification glycine and l-glutamate are also active. 3. The reaction is inhibited strongly by EDTA and N-ethylmaleimide. Substrate analogues, present at concentrations equimolar with respect to the substrates, are not effective as inhibitors. 4. The reaction proceeds in the absence of added cofactors. Magnesium chloride, mercaptoethanol and sucrose stimulate the reaction, and stabilize the activity of the enzyme. 5. The pH optimum of the reaction is 7.0. The K(m) values of glyoxylate and 2-oxoglutarate, at saturating concentration of the corresponding co-substrate, are 16mm and 3.6mm respectively. 6. Isotopic work with specifically labelled [(14)C]glyoxylate and 2-oxo[(14)C]-glutarate suggests that the enzyme system catalyses an initial condensation of glyoxylate and 2-oxoglutarate that results in, or leads to, release of C-1 of both substrates as carbon dioxide. C-2 of glyoxylate and C-5 of 2-oxoglutarate do not appear as carbon dioxide. 7. The stoicheiometry of the reaction is complex. During the initial stages of the reaction, more carbon dioxide is recovered from 2-oxoglutarate than from glyoxylate. Subsequently, there is a disproportionate increase with time of carbon dioxide evolution from the carboxyl group of glyoxylate. The excess of decarboxylation of glyoxylate over 2-oxogluturate is further increased by treatment of reaction products with acid.
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Project description:Serine:glyoxylate aminotransferase (SGAT) converts glyoxylate and serine to glycine and hydroxypyruvate during photorespiration. Besides this, SGAT operates with several other substrates including asparagine. The impact of this enzymatic promiscuity on plant metabolism, particularly photorespiration and serine biosynthesis, is poorly understood. We found that elevated SGAT activity causes surprisingly clear changes in metabolism and interferes with photosynthetic CO2 uptake and biomass accumulation of Arabidopsis. The faster serine turnover during photorespiration progressively lowers day-time leaf serine contents and in turn induces the phosphoserine pathway. Transcriptional upregulation of this additional route of serine biosynthesis occurs already during the day but particularly at night, efficiently counteracting night-time serine depletion. Additionally, higher SGAT activity results in an increased use of asparagine as the external donor of amino groups to the photorespiratory pathway but does not alter leaf asparagine content at night. These results suggest leaf SGAT activity needs to be dynamically adjusted to ensure (i) variable flux through the photorespiratory pathway at a minimal consumption of asparagine and (ii) adequate serine levels for other cellular metabolism.
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Project description:BackgroundSenescence is an important developmental process that leads to the cell death through highly regulated genetically controlled processes in plants. Biotic and abiotic Oxidative stresses can also artificially induce senescence and increase the production of reactive oxygen species (ROS) specifically in chloroplast. One of the important oxidative stresses is paraquat that induces deviation of electron from photosynthesis electron chain and lead to the production of more ROS in chloroplast. Plants have evolved special adoptive mechanism to reallocate nutrient to reproductive and juvenile organs in senescence and different oxidative stresses. Rubisco seems to be the most abundant protein in plants and is involved in many changes during senescence.ResultsIn the present study, the effects of ROS on Rubisco during senescence and oxidative stresses were evaluated by measuring photosynthesis factors such as net photosynthesis rate (Pn), stomatal conductance (G), evaporation rate (E), intra cellular CO2 concentration (Ci), fluorescence and total protein during three stages of development. Our results showed that in paraquat treated plants, CO2 assimilation is the most effective factor that refers to Rubisco damages. The highest correlation and regression coefficient belonged to Ci, while correlation coefficient between photosynthesis rate and total protein was much smaller.ConclusionIt appears in the early stage of oxidative stresses such as exposing to paraquat, ROS has the most effect on Rubisco activity that induces more susceptibility to Rubisco specific protease. Moreover, Rubisco deactivation acts as an initiative signal for Rubisco degradation.
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