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1.
Free radical scavenging behavior of folic acid: evidence for possible antioxidant activity 总被引:8,自引:0,他引:8
Joshi R Adhikari S Patro BS Chattopadhyay S Mukherjee T 《Free radical biology & medicine》2001,30(12):1294-1399
The free radical scavenging properties and possible antioxidant activity of folic acid are reported. Pulse radiolysis technique is employed to study the one-electron oxidation of folic acid in homogeneous aqueous solution. The radicals used for this study are CCl3O2•, N3•, SO4•−, Br2•−, √OH, and O•−. All these radicals react with folic acid under ambient condition at an almost diffusion-controlled rate producing two types of transients. The first transient absorption maximum is around 430 nm, which decays, and a simultaneous growth at around 390 nm is observed. Considering the chemical structure of folic acid, the absorption maximum at 430 nm has been assigned to a phenoxyl radical. The latter one is proposed to be a delocalized molecular radical. A permanent product has been observed in the oxidation of folic acid with CCl3O2• and N3• radicals, with a broad absorption band around 370–400 nm. The bimolecular rate constants for all the radical-induced oxidation reactions of folic acid have been measured. Folic acid is seen to scavenge these radicals very efficiently. In the reaction of thiyl radicals with folic acid, it has been observed that folic acid can not only scavenge thiyl radicals but can also repair these thiols at physiological pH. While carrying out the lipid peroxidation study, in spite of the fact that folic acid is considerably soluble in water, we observed a significant inhibition property in microsomal lipid peroxidation. A suitable mechanism for oxidation of folic acid and repair of thiyl radicals by folic acid has been proposed. 相似文献
2.
Brandsch M 《Amino acids》2006,31(2):119-136
Summary. Membrane transport of L-proline has received considerable attention in basic and pharmaceutical research recently. Of the
most recently cloned members of the solute carrier family, two are “proline transporters”. The amino acid transporter PAT1,
expressed in intestine, kidney, brain and other organs, mediates the uptake of proline and derivatives in a pH gradient-dependent
manner. The Na+-dependent proline transporter SIT1, cloned in 2005, exhibits the properties of the long-sought classical IMINO system. Proline-containing
peptides are of interest for several reasons. Many biologically important peptide sequences contain highly conserved proline
residues. Xaa-Pro peptides are very often resistant to enzymatic hydrolysis and display, in contrast to Pro-Xaa peptides,
a high affinity to the H+/peptide cotransporter PEPT1 which is expressed in intestinal, renal, lung and biliary duct epithelial cells. Furthermore,
several orally available drugs are recognized by PEPT1 as Xaa-Pro analogues due to their sterical resemblance to small peptides. 相似文献
3.
Summary. It was the aim of this study to evaluate the potential of thiolated polycarbophil for the nasal administration of Leucine-enkephalin
(Leu-enkephalin). The enzymatic degradation of Leu-enkephalin on freshly excised bovine nasal mucosa was analysed qualitatively
via thin layer chromatography and quantitatively via high performance liquid chromatography (HPLC). The potential of thiolated
polycarbophil gels to provide a sustained release for the therapeutic peptide was investigated via diffusion studies. Permeation
studies were performed in Ussing-type diffusion chambers with freshly excised bovine nasal mucosa. Results demonstrated that
Leu-enkephalin is mainly degraded by the cleavage of tyrosine from the N-terminus of the peptide. Within one hour more than
63.5 ± 2% of this therapeutic peptide are degraded on the nasal mucosa. In the presence of 0.25% thiolated polycarbophil,
this degradation process, however, could be significantly lowered. Diffusion studies demonstrated that Leu-enkephalin being
incorporated in a 0.5% thiolated polycarbophil gel is sustained released out of it. The appearent permeability coefficient
(Papp) for Leu-enkephalin on the nasal mucosa was determined to be 1.9 ± 1.2 × 10−7 cm/sec. Furthermore, in the presence of 0.5% thiolated polycarbophil and 1% glutathione, which is used as permeation mediator
for the thiomer, the uptake of Leu-enkephalin from the nasal mucosa was even 82-fold improved. According to these results
thiolated polycarbophil might be a promising excipient for nasal administration of Leu-enkephalin. 相似文献
4.
Summary. Amino acids react with methylglyoxal to form advanced glycation end products. This reaction is known to produce free radicals.
In this study, cleavage to plasmid DNA was induced by the glycation of lysine with methylglyoxal in the presence of iron(III).
This system was found to produce superoxide as well as hydroxyl radicals. The abilities of various vitamins to prevent damage
to plasmid DNA were evaluated. Pyridoxal-5-phosphate showed maximum protection, while pyridoxamine showed no protection. The
protective abilities could be directly correlated to inhibition of production of hydroxyl and superoxide radicals. Pyridoxal-5-phosphate
exhibited low radical scavenging ability as evaluated by its TEAC, but showed maximum protection probably by interfering in
free radical production. Pyridoxamine did not inhibit free radical production. Thiamine and thiamine pyrophosphate, both showed
protective effects albeit to different extents. Tetrahydrofolic acid showed better antioxidant activity than folic acid but
was found to damage DNA by itself probably by superoxide generation. 相似文献
5.
Bartesaghi S Ferrer-Sueta G Peluffo G Valez V Zhang H Kalyanaraman B Radi R 《Amino acids》2007,32(4):501-515
Summary. In this review we address current concepts on the biological occurrence, levels and consequences of protein tyrosine nitration
in biological systems. We focused on mechanistic aspects, emphasizing on the free radical mechanisms of protein 3-nitrotyrosine
formation and critically analyzed the restrictions for obtaining large tyrosine nitration yields in vivo, mainly due to the
presence of strong reducing systems (e.g. glutathione) that can potently inhibit at different levels the nitration process.
Evidence is provided to show that the existence of metal-catalyzed processes, the assistance of nitric oxide-dependent nitration
steps and the facilitation by hydrophobic environments, provide individually and/or in combination, feasible scenarios for
nitration in complex biological milieux. Recent studies using hydrophobic tyrosine analogs and tyrosine-containing peptides
have revealed that factors controlling nitration in hydrophobic environments such as biomembranes and lipoproteins can differ
to those in aqueous compartments. In particular, exclusion of key soluble reductants from the lipid phase will more easily
allow nitration and lipid-derived radicals are suggested as important mediators of the one-electron oxidation of tyrosine
to tyrosyl radical in proteins associated to hydrophobic environments. Development and testing of hydrophilic and hydrophobic
probes that can compete with endogenous constituents for the nitrating intermediates provide tools to unravel nitration mechanisms
in vitro and in vivo; additionally, they could also serve to play cellular and tissue protective functions against the toxic
effects of protein tyrosine nitration. 相似文献
6.
Amy Bogaard 《Vegetation History and Archaeobotany》2002,11(1-2):155-168
Despite widespread criticism, the shifting cultivation model continues to inform discussion of Neolithic farming in Europe,
beginning with early Neolithic (Linearbandkeramik or LBK) communities concentrated in the loess belt of western-central Europe. Hundreds of LBK and later Neolithic sites have
been excavated in this region and many of them sampled for charred plant remains. Archaeobotanical data on the weed floras
harvested with crops provide the most direct archaeological evidence of crop husbandry practices, including the permanence
of crop fields, but have played a limited role in the debate over shifting cultivation. The Hambach Forest experiment, conducted
in the 1970s-80s near Cologne, Germany, provides valuable comparative data on the weed floras growing in newly cleared cultivation
plots in an area of longlived mixed oak woodland on loess-based soil. Correspondence analysis of the Hambach weed survey data
suggests that weed floras of fields managed under a shifting cultivation regime would be rich in perennial species, including
woodland perennials. Comparison of these results with Neolithic weed assemblages from the loess belt of western-central Europe
strongly suggests that Neolithic crop fields were not recently cleared of woodland vegetation but were long-established.
Received September 5, 2001 / Accepted February 26, 2002 相似文献
7.
Summary. Sulfenic acid (RSOH) is a central intermediate in both the reversible and irreversible redox modulation by reactive species
of an increasing number of proteins involved in signal transduction and enzymatic pathways. In this paper we focus on human
serum albumin (HSA), the most abundant plasma protein, proposed to serve antioxidant functions in the vascular compartment.
Sulfenic acid in HSA has been previously detected using different methods after oxidation of its single free thiol Cys34 through
one- or two-electron mechanisms. Since recent evidence suggests that sulfenic acid in HSA is stabilized within the protein
environment, this derivative represents an appropriate model to examine protein sulfenic acid biochemistry, structure and
reactivity. Sulfenic acid in HSA could be involved in mixed disufide formation, supporting a role of HSA-Cys34 as an important
redox regulator in extracellular compartments. 相似文献
8.
Lucyna Kubiak-Martens 《Vegetation History and Archaeobotany》2002,11(1-2):23-32
Roots and tubers, together with other plant storage organs such as rhizomes, bulbs, corms, etc. are known to be a source
of human food. Until very recently, however, remains of root foods were rarely identified from archaeological contexts in
temperate Europe. New evidence for the use of root foods has been recently recovered from the early Erteb?lle settlement at
Halsskov in Denmark. Remains included charred bulbs of Allium cf. ursinum and tubers of Conopodium majus. They were accompanied by charred remains of parenchymatous tissues derived from underground parts of other plants. All parenchymatous
remains were recovered from features that could be interpreted as pit-cooking depressions. A minimum of two periods of root
food gathering can be assumed, spring to early summer and autumn. The presence of charred seeds of Nuphar pumilum suggests that either the seeds or rhizomes (or both) were use as food.
Received September 4, 2001 / Accepted February 27, 2002 相似文献
9.
Summary. Recent literature suggests that both caffeine and taurine can induce diuresis and natriuresis in rat and man. Although they
act via different cellular mechanisms, their diuretic actions might be additive. This is of considerable interest, as several
commercially available energy drinks contain both substances.
In this study we examined the possible diuretic effects of caffeine and taurine in a cross-over-design in which 12 healthy
male volunteers received each of 4 different test drinks (750 ml of energy drink containing 240 mg caffeine and 3 g taurine,
the three other test drinks either lacked caffeine, taurine or both) after restraining from fluids for 12 h.
Mixed model analyses demonstrated that urinary output and natriuresis were significantly increased by caffeine (mean differences
243 ml and 27 mmol; both p < 0.001) and that there were no such effects of taurine (mean differences 59 ml and −4 mmol). Additionally, urinary osmolarity
at baseline was significantly related to the urinary output (p < 0.001). Urine osmolarity values at baseline and in the 6 h urine collection did not differ significantly between treatments.
Taken together, our study demonstrates that diuretic and natriuretic effects of the tested energy drink were largely mediated
by caffeine. Taurine played no significant role in the fluid balance in moderately dehydrated healthy young consumers. Consequently,
the diuretic potential of energy drinks will not differ significantly from other caffeine containing beverages. 相似文献
10.
Summary. Glutamine is one of the most abundant free amino acid found in raw food. In this study, the contribution of free glutamine
to nonenzymatic browning and fluorescence was investigated using an aqueous model system with methylglyoxal. The results indicated
that glutamine contributed to the Maillard reaction via two pathways. First, the hydrolysis of the amide bond of glutamine
led to the release of ammonia which was implicated in the formation of brown color and fluorescence. Among other nitrogen
donors tested (asparagine, glutamic acid and urea) our results demonstrated that free glutamine was a major source of ammonia
during heating. When heated at 120 and 180 °C, 100% of ammonia was released from glutamine after 60 and 10 min, respectively.
The second pathway involved a direct Maillard reaction with the α-amino group of glutamine. Both pathways led to a rapid and
complete destruction of glutamine when heated in the model systems. With reference to the Maillard browning (absorbance at
420 nm) glutamine turned out to be the most reactive amine, followed by asparagine, glutamate, ammonia and urea. Maximum fluorescence
(excitation and emission wavelengths at 330 and 450 nm, respectively) was also observed with glutamine followed by urea and
ammonia. Overall this study suggested that free glutamine predominantly contributes to the color and fluorescence formations
of foodstuffs. 相似文献
11.
Summary. Lipid-protein adducts are formed during oxidative and nitrative stress conditions associated with increasing lipid and protein
oxidation and nitration. The focus of this review is the analysis of interactions between oxidative-modified lipids and proteins
and how lipid nitration can modulate lipid-protein adducts formation. For this, two biologically-relevant models will be analysed:
a) human low density lipoprotein, whose oxidation is involved in the early steps of atherogenesis, and b) α-synuclein/lipid
membranes system, where lipid-protein adducts are being associated with the develop of Parkinson disease and other synucleinopathies. 相似文献
12.
13.
Reyes-Toso CF Rebagliati IR Ricci CR Linares LM Albornoz LE Cardinali DP Zaninovich A 《Amino acids》2006,31(3):299-302
Summary. The objective of this study was to examine the in vivo effect of melatonin on rat mitochondrial liver respiration. Two experiments were performed: For experiment 1, adult male
rats received melatonin in the drinking water (16 or 50 μg/ml) or vehicle during 45 days. For experiment 2, rats received
melatonin in the drinking water (50 μg/ml) for 45 days, or the same amount for 30 days followed by a 15 day-withdrawal period.
At sacrifice, a liver mitochondrial fraction was prepared and oxygen consumption was measured polarographically in the presence
of excess concentration of DL-3-β-hydroxybutyrate or L-succinate. Melatonin treatment decreased Krebs’ cycle substrate-induced
respiration significantly at both examined doses. The stimulation of mitochondrial respiration caused by excess concentration
of substrate recovered after melatonin withdrawal. Basal state 4 respiration was not modified by melatonin. Melatonin, by
curtailing overstimulation of cellular respiration caused by excess Krebs’ cycle substrates, can protect the mitochondria
from oxidative damage. 相似文献
14.
Antioxidant mechanisms of isoflavones in lipid systems: paradoxical effects of peroxyl radical scavenging 总被引:15,自引:0,他引:15
Rakesh P. Patel Brenda J. Boersma Jack H. Crawford Neil Hogg Marion Kirk Balaraman Kalyanaraman Dale A. Parks Stephen Barnes Victor Darley-Usmar 《Free radical biology & medicine》2001,31(12):1570-1581
Oxidation of lipids has been implicated in the pathophysiology of atherosclerosis. It has been suggested that scavenging of lipid peroxyl radicals contribute to the antiatherosclerotic effects of naturally occurring compounds such as the isoflavones. This group of polyphenolics includes genistein and is present in relatively high concentrations in food products containing soy. Soy isoflavones are capable of inhibiting lipoprotein oxidation in vitro and suppressing formation of plasma lipid oxidation products in vivo. However, key aspects of the antioxidant mechanisms remain unknown. In this study the antioxidant effects of genistein and other soy isoflavones on lipid peroxidation initiated by mechanistically diverse oxidants was investigated. Although isoflavones inhibited lipid peroxidation stimulated by both metal-dependent and independent processes, the concentration required for these effects were relatively high compared to those found in vivo. Interestingly, however, isoflavones were not consumed and remained in the native state over the time during which inhibition of lipid peroxidation was observed. This was also the case under conditions where synergistic inhibition of LDL oxidation was observed with ascorbate. Furthermore, in an oxidation system driven solely by peroxyl radicals, isoflavones were found to be relatively poor peroxyl radical scavengers. Consistent with the apparent lack of reactivity with lipid-derived oxidants, isoflavones were also relatively resistant to oxidation mediated by the potent oxidant peroxynitrite. The potential antioxidant mechanisms of isoflavones are discussed in the context of possible reactivities of isoflavone-derived phenoxyl radicals. 相似文献
15.
Summary. The reactions of Leu- and Met-enkephalin (Tyr-Gly-Gly-Phe-Leu/Met) with fructose resulted in the parallel formation of Heyns
compounds (N-peptidyl-d-mannosamine and -d-glucosamine) and sugar-peptide generated imidazolidinone diastereomers. Glucose showed higher level of reactivity than fructose
with respect to the extent of glycated product formation. The presence of fructose in the incubation mixtures makes Met residue
more susceptible to oxidation than glucose.
Authors’ address: Dr. Štefica Horvat, Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, POB 180, 10002
Zagreb, Croatia 相似文献
16.
The function of the Na,K-ATPase is
known to be considerably impaired in the presence of free radicals such
as OH•. While previous experiments were largely based
on the loss of enzymatic activity of the protein, this is the first
communication dealing with partial reactions of the pump cycle in the
presence of free radicals produced by water radiolysis. Three
different system states, which are directly involved in ion transfer
catalyzed by the enzyme, showed similar sensitivity to free radical
action. This is indicated by largely identical D37-doses
of the decay of the reaction amplitudes investigated. The decrease
in the efficiency of the enzyme functions was largely due to a lethal
damage of pump molecules. A kinetic analysis of the ATP-induced
conformational transition E1→ E2 revealed,
however, that a minor component of the inactivation is due to a
reduction of the transition rate constant. The decrease of the
enzymatic activity could be simulated by the decay of the rate-limiting
conformational transition. This finding indicates the conservation
of a close coupling between ATP-hydrolysis and sodium translocation
process throughout free-radical induced inactivation. As a result
of the tight coupling, enzyme modification at different system states
leads to similar functional consequences for the protein.
Received: 19 July 1996/Revised: 21 October 1996 相似文献
17.
Summary. Mammalian hexokinase (HXK) is found at the outer mitochondrial membrane, exposed to mitochondrial oxygen- and nitrogen-radicals.
Given the important role of this enzyme in metabolic pathways and diseases, the effect of S-nitrosoglutathione (GSNO) on HXK A structure and activity was studied. To focus on the catalytic domain, yeast HXK A was
used because it has a significant homology to the mammalian domain that contains both the regulatory and catalytic sites.
Biologically relevant [GSNO]/[HXK] caused a significant decrease in Vmax with glucose (but not with fructose), along with oxidation of 5 Met and nitration of 4 Tyr. Preincubation of HXK with glucose
abrogated the effect of GSNO whereas fructose was ineffective. These results are interpreted by considering the tight binding
of glucose to the enzyme as opposed to that of fructose. The segment comprised from amino acids 304 to 306 contained the most
modifications. Given that this sequence is highly conserved in HXK from various species, a decline in activity is expected
when a high-affinity substrate is presented.
Considering that changes in primary structure are envisioned at high [GSNO]/[HXK] ratios, like those present under normal
conditions, it could be hypothesized that the high concentration of hexokinase present in fast growing tumors may serve not
only to sustain high glycolysis rates, but also to minimize protein damage that might result in activity decline, compromising
energy metabolism. 相似文献
18.
First archaeological evidence of banana cultivation in central Africa during the third millennium before present 总被引:1,自引:0,他引:1
Christophe Mbida Mindzie Hughes Doutrelepont Luc Vrydaghs Rony L. Swennen Rudy J. Swennen Hans Beeckman Edmond de Langhe Pierre de Maret 《Vegetation History and Archaeobotany》2001,10(1):1-6
Phytoliths recovered from refuse pits excavated in central Cameroon and dated to ca 2500 B.P. have been positively identified
for the first time in Africa as derived from Musa the cultivated banana, after a comparative study of Musa and Ensete phytoliths. This discovery provides archaeologists with unequivocal proof of early agriculture in central Africa. Furthermore,
the presence of banana in Cameroon much earlier than previously assumed could explain how agriculture spread through the rain
forest. Lastly, as Musa is of Asian origin, this study provides the first concrete evidence of contacts across the Indian Ocean a millennium earlier
than currently accepted.
Received July 12, 1999 / Accepted May 4, 2000 相似文献
19.
Reactive oxygen species, when released under controlled conditions and limited amounts, contribute to cellular proliferation, senescence, and survival by acting as signaling intermediates. In past decades there has been an epidemic diffusion of nonalcoholic fatty liver disease (NAFLD) that represents the result of the impairment of lipid metabolism, redox imbalance, and insulin resistance in the liver. To date, most studies and reviews have been focused on the molecular mechanisms by which fatty liver progresses to steatohepatitis, but the processes leading toward the development of hepatic steatosis in NAFLD are not fully understood yet. Several nuclear receptors, such as peroxisome proliferator-activated receptors (PPARs) α/γ/δ, PPARγ coactivators 1α and 1β, sterol-regulatory element-binding proteins, AMP-activated protein kinase, liver-X-receptors, and farnesoid-X-receptor, play key roles in the regulation of lipid homeostasis during the pathogenesis of NAFLD. These nuclear receptors may act as redox sensors and may modulate various metabolic pathways in response to specific molecules that act as ligands. It is conceivable that a redox-dependent modulation of lipid metabolism, nuclear receptor-mediated, could cause the development of hepatic steatosis and insulin resistance. Thus, this network may represent a potential therapeutic target for the treatment and prevention of hepatic steatosis and its progression to steatohepatitis. This review summarizes the redox-dependent factors that contribute to metabolism alterations in fatty liver with a focus on the redox control of nuclear receptors in normal liver as well as in NAFLD. 相似文献