The chemistry of lipid alkoxyl radicals and their role in metal-amplified lipid peroxidation

1995 ◽  
Vol 61 ◽  
pp. 65-72 ◽  
Author(s):  
Lawrence J. Marnett ◽  
Allan L. Wilcox
Keyword(s):  
Lipid Peroxidation ◽  
Steady State ◽  
Fatty Acid ◽  
Hydroxyl Radical ◽  
Metal Complexes ◽  
Polyunsaturated Fatty Acid ◽  
Ring Opening ◽  
Steady State Concentration ◽  
State Concentration ◽  
Fatty Acid Hydroperoxides

Reaction of polyunsaturated fatty acid hydroperoxides with metal complexes generates lipid alkoxyl radicals and metal-oxo complexes. Lipid alkoxyl radicals are presumed to be the species responsible for metal-amplified lipid peroxidation because of the chemical analogy of simple organic alkoxyl radicals to the hydroxyl radical. However, polyunsaturated fatty acid alkoxyl radicals exhibit a rich and diverse chemistry that is dominated by intramolecular cyclization to epoxyallylic radicals. Studies described herein demonstrate that the equilibrium between cyclization and ring-opening of epoxyallylic radicals lies overwhelmingly toward cyclization. Thus lipid alkoxyl radicals have a steady-state concentration that is so low that their contribution to metal-amplified lipid peroxidation is insignificant. In fact, the species responsible for metal amplification of lipid peroxidation appears to be the epoxyperoxyl radical formed by coupling the epoxyallylic radical to molecular oxygen.

scholarly journals A Caleosin-Like Protein with Peroxygenase Activity Mediates Aspergillus flavus Development, Aflatoxin Accumulation, and Seed Infection

2015 ◽  
Vol 81 (18) ◽  
pp. 6129-6144 ◽  
Author(s):  
Abdulsamie Hanano ◽  
Ibrahem Almousally ◽  
Mouhnad Shaban ◽  
Elizabeth Blee
Keyword(s):  
Fatty Acid ◽  
Aspergillus Flavus ◽  
Polyunsaturated Fatty Acid ◽  
Calcium Binding ◽  
Antioxidant Activities ◽  
Fungal Growth ◽  
Oxidation Reactions ◽  
Content Type ◽  
Fatty Acid Hydroperoxides

ABSTRACTCaleosins are a small family of calcium-binding proteins endowed with peroxygenase activity in plants. Caleosin-like genes are present in fungi; however, their functions have not been reported yet. In this work, we identify a plant caleosin-like protein inAspergillus flavusthat is highly expressed during the early stages of spore germination. A recombinant purified 32-kDa caleosin-like protein supported peroxygenase activities, including co-oxidation reactions and reduction of polyunsaturated fatty acid hydroperoxides. Deletion of the caleosin gene prevented fungal development. Alternatively, silencing of the gene led to the increased accumulation of endogenous polyunsaturated fatty acid hydroperoxides and antioxidant activities but to a reduction of fungal growth and conidium formation. Two key genes of the aflatoxin biosynthesis pathway,aflRandaflD, were downregulated in the strains in whichA. flavusPXG(AfPXG) was silenced, leading to reduced aflatoxin B1 productionin vitro. Application of caleosin/peroxygenase-derived oxylipins restored the wild-type phenotype in the strains in whichAfPXGwas silenced.PXG-deficientA. flavusstrains were severely compromised in their capacity to infect maize seeds and to produce aflatoxin. Our results uncover a new branch of the fungal oxylipin pathway and may lead to the development of novel targets for controlling fungal disease.

Divergent effects of intravenous GSH and cysteine on renal and hepatic GSH

1992 ◽  
Vol 263 (2) ◽  
pp. R348-R352 ◽  
Author(s):  
S. Aebi ◽  
B. H. Lauterburg
Keyword(s):  
Steady State ◽  
De Novo ◽  
Feedback Inhibition ◽  
Therapeutic Use ◽  
Steady State Concentration ◽  
De Novo Synthesis ◽  
State Concentration ◽  
Cellular Thiol

There is a growing interest in the therapeutic use of sulfhydryls. To assess the effect of glutathione (GSH) and cysteine on the cellular thiol status, thiols were administered intravenously to rats in doses ranging from 1.67 to 8.35 mmol/kg with and without pretreatment with 4 mmol/kg buthionine-[S,R]-sulfoximine (BSO), an inhibitor of GSH synthesis. One hour after administration of 1.67 mmol/kg GSH, the concentration of GSH rose from 5.2 +/- 1.0 to 8.4 +/- 0.9 mumol/g and from 2.5 +/- 0.5 to 3.7 +/- 0.7 mumol/g in liver and kidneys, respectively. After 8.35 mmol/kg, hepatic GSH did not increase further, but renal GSH rose to 6.7 +/- 1.8 mumol/g. Infusion of cysteine increased hepatic GSH to the same extent as intravenous GSH, but renal GSH did not increase after 1.67 mmol/kg and even significantly decreased to 0.6 +/- 0.2 mumol/g after 8.35 mmol/kg. In the presence of BSO, GSH resulted in a significant increase in renal but not hepatic GSH, suggesting that the kidneys take up intact GSH and indicating that the increment in hepatic GSH was due to de novo synthesis. The present data show that hepatic GSH can be markedly increased in vivo by increasing the supply of cysteine. Measurements of hepatic cysteine indicate that up to a concentration of approximately 0.5 mumol/g cysteine is a key determinant of hepatic GSH, such that the physiological steady-state concentration of GSH in the liver appears to be mainly determined by the availability of cysteine. At higher concentrations GSH does not increase further, possibly due to feedback inhibition of GSH synthesis or increased efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of oxidative stress during imbibition of soybean embryonic axes

1994 ◽  
Vol 102 ◽  
pp. 279-286 ◽  
Author(s):  
Susana Puntarulo
Keyword(s):  
Oxidative Stress ◽  
Steady State ◽  
External Medium ◽  
Tocopherol Content ◽  
Active Species ◽  
Oxygen Species ◽  
Steady State Concentration ◽  
Embryonic Axes ◽  
State Concentration

SynopsisBoth respiration and generation by soybean embryonic axes showed a sharp increase upon germination, leading to a significant increase in the steady-state concentration of and H2O2 after 6 h of imbibition. An assay was developed to assess in vivo generation of reactive oxygen species, based upon DCFH-DA oxidation. Fluorescence of the external medium was dependent on reaction time and axes number and was inhibited by catalase.α-Tocopherol content declined significantly after 24 h of incubation, as compared to the content at the onset of germination. Incubation in the presence of redox cycling agent paraquat (4 mM) for 24 h increased α-tocopherol content to 1.9±0.2 nmol per axis from 1.0 ± 0.1 nmol per axis in the absence of paraquat. Supplementation of the incubation medium with 500 μM Fe-EDTA increased α-tocopherol content to 1.8±0.1 nmol/axis and DCFH-DA oxidation by two-fold.The data presented here showed that active metabolism at the onset of germination increased steady-state concentration of oxygen active species and suggest that cellular content of α-tocopherol is physiologically adjusted as a response to conditions of oxidative stress.

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