Degradation of Ovalbumin by L-Ascorbic Acid in the Presence of Cupric Ion

Ovalbumin, L-ascorbic acid and cupric sulfate were allowed to react at pH 3.0, 6.0, 6.8 and 7.5. Non-proteinous nitrogen compounds were formed from ovalbumin coupled with autoxidation of ascorbic acid, and a pronounced increase in their formation was observed in the reactions of neutral pH ranges. Non-proteinous nitrogen compounds contained peptides, free amino acids and ammonia. In the reactions of ovalbumin with triose reductone similar results to those with ascorbic acid were obtained. In the ovalbumin degraded with ascorbic acid at pH 6.8 was found an increase of N-terminal amino acid, which could react with carbonyl compounds resulting in browning.     

Effect of polar solvents on beta-carotene radical precursor

Beta-carotene forms radicals in chloroform upon photo-excitation (i) in the femtosecond time-scale by direct electron ejection into chloroform and (ii) in the microsecond time-scale by secondary reactions with chloroform radicals formed in the faster reactions. The precursor for beta-carotene radical cation decays in a second-order reaction in the mixed solvents, with a rate decreasing for increasing dielectric constant of cosolvent (acetic acid < ethanol < acetonitrile approximately methanol). The precursor is assigned as an ion pair from which the beta-carotene radical cation is formed in neat chloroform, but in more polar solvents it reacts at least partly through disproportionation in a bimolecular reaction promoted by the presence of ions. The stabilization of the radical precursor by increased solvent polarity, allowing for deactivation of the precursor by an alternative reaction channel, is discussed in relation to the balance of pro- and antioxidative properties of beta-carotene at lipid/water interfaces.     

In vitro antioxidant studies of Sphaeranthus indicus (Linn)

The free radical scavenging potential of the plant S. indicus was studied by using different antioxidant models of screening. The ethanolic extract at 1000 microg/ml showed maximum scavenging of the radical cation, 2,2-azinobis-(3-ethylbenzothiazoline-6-sulphonate) (ABTS) observed upto 41.99% followed by the scavenging of the stable radical 1,1-diphenyl, 2-picryl hydrazyl (DPPH) (33.27%), superoxide dismutase (25.14%) and nitric oxide radical (22.36%) at the same concentration. However, the extract showed only moderate scavenging activity of iron chelation (14.2%). Total antioxidant capacity of the extract was found to be 160.85 nmol/g ascorbic acid. The results justify the therapeutic applications of the plant in the indigenous system of medicine, augmenting its therapeutic value.     

Antioxidant potential of aminothiazole derivative and its protective effect on H2O2-induced oxidative damage on pBR322 DNA and RBC cellular membrane

The present work was carried out to evaluate the antioxidant and free radical scavenging activity of aminothiazole derivative by performing various in vitro assays; to study its protective effect on H(2)O(2)-induced oxidative damage on pBR322 DNA and on RBC cellular membrane. The in vitro assays were performed with different concentrations of aminothiazole derivative (6.15, 12.29, 18.44, 24.59, and 30.73 microM) and the results were compared with standards like ascorbic acid and trolox. Our results clearly indicated that aminothiazole derivative at a dose of 18.44 microM exhibited radical scavenging activity greater than that of ascorbic acid and trolox. The DNA protective effect on pBR322 DNA showed that there was a concentration-dependent inhibition of the disappearance of supercoiled (ccc) form of DNA on incubation with 30 mM H(2)O(2) in the presence of different concentrations of aminothiazole derivative. Thus our compound at 1.5 mM prevents the conversion from supercoiled (ccc) form to open circular form (oc) form of pBR322 DNA. Pretreatment with aminothiazole derivative at a dose of 18.44 microM prevents membrane damage and exhibits an IC(50) value, which is the concentration of the sample required to inhibit 50% of the radical formed greater than that of the standards (ascorbic acid and trolox). Thus our compound of interest aminothiazole derivative exhibits antioxidant and free radical scavenging properties greater than that of standards like ascorbic acid and trolox and thereby protects pBR322 DNA and RBC cellular membrane from free radical induced oxidative damage.     

Peroxidase catalysed formation of cytotoxic prooxidant phenothiazine free radicals at physiological pH

The antipsychotic phenothiazines may have other therapeutic applications because of their ability to kill bacteria, plasmids and tumor cells. They are also known to undergo a peroxidase-catalysed oxidation to form cation radicals that are stable at acid pH, but are not detected at a neutral pH. The objective of this project was to determine whether phenothiazine cation radical metabolites could cause oxidative stress at a neutral pH resulting in cytotoxicity. At a neutral pH, catalytic amounts of phenothiazines were found to be oxidised by a peroxidase/H2O2 system and also caused ascorbate, GSH and NADH cooxidation. NADH and GSH co-oxidation was accompanied by oxygen uptake and was increased by the addition of catalytic amounts of superoxide dismutase, indicating that the superoxide radical was formed. The phenothazines were different from other peroxidase substrates in that the NADH, ascorbate or GSH cooxidation was faster at pH 6.0 than pH 7.4, thereby partly reflecting the cation radical stability. The order of catalytic effectiveness found was promazine > chlorpromazine > trifluoperazine. Peroxidase/H2O2 also markedly increased phenothiazine cytotoxicity towards isolated rat hepatocytes at nontoxic phenothiazine concentrations. At both pH 6.0 and 7.4, the same order of phenothiazine catalytic effectiveness was observed as seen in the co-oxidation experiments. Cytotoxicity to hepatocytes could be attributed to oxidative stress as most hepatocyte glutathione oxidation and lipid peroxidation preceded phenothiazine induced cytotoxicity and that cytotoxicity was prevented by the antioxidant butylated hydroxyanisole. This hepatocyte/peroxidase/H2O2 system could be a useful model for studying drug induced idiosyncratic hepatic injury enhanced by inflammation.     

Melatonin and structurally-related,endogenous indoles act as potent electron donors and radical scavengers in vitro

Summary

The radical scavenging properties of melatonin, structurally-related indoles and known antioxidants were investigated in kinetic competition studies using the specific radical trapping reagent 2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS). In the presence of highly reactive radicals, ABTS is oxidized to the stable thiazoline cation radical, ABTS*⁺ which, due to its intense green color, can be measured photometrically at 420 nm absorbance. The indoles melatonin, 5-methoxytryptophol, 5-methoxyindole acetic acid and 5-methoxytryptamine as well as the phenolic and thiolic antioxidants ascorbic acid, Trolox, and glutathione inhibited ABTS cation radical formation and catalyzed ABTS radical cation reduction. Melatonin was the most potent radical scavenger and electron donor when compared with the methoxylated indole analogs and the other antioxidants tested. Melatonin, the methoxylated indole analogs and the other antioxidants tested acted as potent electron donors which scavenged initiating and propagating radicals and repaired oxidative damage due to electrophile intermediates.     

Ovothiols as free-radical scavengers and the mechanism of ovothiol-promoted NAD(P)H-O2 oxidoreductase activity

Racemic ovothiol A [(+/-)-1a] and the ovothiol model compound 1,5-dimethyl-4-mercaptoimidazole (DMI, 2) were found to scavange the free radicals Fremy's salt (4) and Banfield' radical (5) much more rapidly than did the thiol antioxidant glutathione. Ovothiol A also scavenges the tyrosyl radical, with efficiency comparable to that of ascorbic acid and the tocopherol analogue trolox (3). The ovothiol model compound DMI was found to scavenge superoxide with a rate constant comparable to that of the reaction between superoxide and glutathione. These results suggest both a free-radical scavenging role for the ovothiols and a mechanism by which the ovothiols confer NAD(P)H-O2 oxidoreductase activity upon the enzyme ovoperoxidase. Investigation of this mechanism implicates the ovothiol thiyl radical and the NAD radical as key intermediates. The ovothiyl radical appears to be unreactive toward oxygen but highly reactive toward NADH. An estimate of the one-electron oxidation potential of the ovothiol anion is presented. The physical basis for the stability of the ovothiol free radical is discussed.     

Antioxidant potential of ferulic acid.

Ferulic acid is a ubiquitous plant constituent that arises from the metabolism of phenylalanine and tyrosine. It occurs primarily in seeds and leaves both in its free form and covalently linked to lignin and other biopolymers. Due to its phenolic nucleus and an extended side chain conjugation, it readily forms a resonance stabilized phenoxy radical which accounts for its potent antioxidant potential. UV absorption by ferulic acid catalyzes stable phenoxy radical formation and thereby potentiates its ability to terminate free radical chain reactions. By virtue of effectively scavenging deleterious radicals and suppressing radiation-induced oxidative reactions, ferulic acid may serve an important antioxidant function in preserving physiological integrity of cells exposed to both air and impinging UV radiation. Similar photoprotection is afforded to skin by ferulic acid dissolved in cosmetic lotions. Its addition to foods inhibits lipid peroxidation and subsequent oxidative spoilage. By the same mechanism ferulic acid may protect against various inflammatory diseases. A number of other industrial applications are based on the antioxidant potential of ferulic acid.     

Free radical scavenging behavior of folic acid: evidence for possible antioxidant activity

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.     

Isolation of quercetin's salts and studies of their physicochemical properties and antioxidant relationships

Hydroxyflavones in alkaline solutions show high free radical scavenging activities. Quercetin, one of these hydroxyflavones may be submitted to chemical reactions yielding a mixture of mono-, di- and tri-sodium salts. These salts were recovered after solubilization and stepwise precipitation in methylalcohol/ethylacetate solvents. The different salts were analyzed using sodium emission spectrophotometry and nuclear magnetic resonance to determine the number of acid hydrogens at pH10 and the position of these acid hydrogens. Our study demonstrates that among the three salts of quercetin, the di-sodium compound is endowed with the more efficient scavenging properties in a phosphate buffer at physiological pH7.4. Physicochemical parameters and free hydroxyl radical scavenging activity relationships were also determined, allowing to explain the mechanisms whereby hydroxyl groups exert their radical scavenging activities.     

Lipid peroxyl radical intermediates in the peroxidation of polyunsaturated fatty acids by lipoxygenase. Direct electron spin resonance investigations

Lipid peroxyl radicals resulting from the peroxidation of polyunsaturated fatty acids by soybean lipoxygenase were directly detected by the method of rapid mixing, continuous-flow electron spin resonance spectroscopy. When air-saturated borate buffer (pH 9.0) containing linoleic acid or arachidonate acid was mixed with lipoxygenase, fatty acid-derived peroxyl free radicals were readily detected; these radicals have a characteristic g-value of 2.014. An organic free radical (g = 2.004) was also detected; this may be the carbon-centered fatty acid free radical that is the precursor of the peroxyl free radical. The ESR spectrum of this species was not resolved, so the identification of this free radical was not possible. Fatty acids without at least two double bonds (e.g. stearic acid and oleic acid) did not give the corresponding peroxyl free radicals, suggesting that the formation of bisallylic carbon-centered radicals precedes peroxyl radical formation. The 3.8-G doublet feature of the fatty acid peroxyl spectrum was proven (by selective deuteration) to be a hyperfine coupling due to a gamma-hydrogen that originated as a vinylic hydrogen of arachidonate. Arachidonate peroxyl radical formation was shown to be dependent on the substrate, active lipoxygenase, and molecular oxygen. Antioxidants are known to protect polyunsaturated fatty acids from peroxidation by scavenging peroxyl radicals and thus breaking the free radical chain reaction. Therefore, the peroxyl signal intensity from micellar arachidonate solutions was monitored as a function of the antioxidant concentration. The reaction of the peroxyl free radical with Trolox C was shown to be 10 times slower than that with vitamin E. The vitamin E and Trolox C phenoxyl radicals that resulted from scavenging the peroxyl radical were also detected.     

Effect of food reductones on the generation of the pyrazine cation radical and on the formation of the mutagens in the reaction of glucose, glycine and creatinine

One of the possible pathways of the formation of mutagens in heated foods is through the pyrazine cation radical generated in the early stage of the Maillard reaction. The aim of the present study was to elucidate how food reductones contribute to the pyrazine cation radical generation in the reaction of glucose (Glc) and glycine (Gly), and to the formation of the mutagens in the reaction of Glc, Gly and creatinine. Electron spin resonance (ESR) studies showed that fragrant reductones, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF), generated in the Maillard reactions, enhanced the generation of the pyrazine cation radical in the reaction of Glc and Gly, and the reaction of DMHF or HEMF with Gly generated a larger amount of the pyrazine cation radical than the reaction of Glc and Gly, indicating that the furanones were intermediates of the pyrazine cation radical. By contrast, food antioxidants, ascorbic acid and erythorbic acid, effectively scavenged the pyrazine cation radical generated in the reaction of Glc and Gly. DMHF and HEMF were not effective to modulate the mutagen formation in the reaction of Glc, Gly and creatinine, and the mutagenicity produced in the reaction of DMHF or HEMF, Gly and creatinine was lower than that produced in the reaction of Glc, Gly and creatinine. On the other hand, ascorbic acid and erythorbic acid were effective to decrease the mutagen formation in the reaction of Glc, Gly and creatinine.     

A physiochemical mechanism of hemozoin (beta-hematin) synthesis by malaria parasite.

Malaria parasite homogenate, the lipid extracts, and an unsaturated fatty acid, linoleic acid, which have been shown to promote beta-hematin formation in vitro, were used to investigate the mechanism of hemozoin biosynthesis, a distinct metabolic function of the malaria parasite. In vitro beta-hematin formation promoted by Plasmodium yoelii homogenate, the lipid extracts, and linoleic acid were blocked by ascorbic acid, reduced glutathione, sodium dithionite, beta-mercaptoethanol, dithiothreitol, and superoxide dismutase. Oxidized glutathione did not show any effect. Preoxidized preparations of the lipids extracts or the P. yoelii homogenate failed to catalyze beta-hematin formation. Depletion of oxygen in the reaction mixtures also inhibited the lipid-catalyzed beta-hematin formation. Under the reaction conditions similar to those used for the in vitro beta-hematin formation assay, the antioxidants and reducing agents mentioned above, except the DTT and beta-mercaptoethanol, did not cause degradation of heme. beta-Hematin formation was also inhibited by p-aminophenol, a free radical chain reaction breaker. Hemozoin biosynthesis within the digestive vacuoles of the malaria parasite may be a lipid-catalyzed physiochemical reaction. An oxidative mechanism may be proposed for lipid-mediated beta-hematin formation, which may be mediated by generation of some free radical intermediates of heme.     

Vitamin C (ascorbic acid) induced hydroxyl radical formation in copper contaminated household drinking water: role of bicarbonate concentration

We have previously shown that Vitamin C (ascorbic acid) can trigger hydroxyl radical formation in copper contaminated household drinking water. We report here that the capacity of ascorbic acid to catalyze hydroxyl radical generation in the drinking water samples is strongly dependent on the bicarbonate concentration (buffer capacity and pH) of the samples. We found that at least 50 mg/l bicarbonate was required in the water samples to maintain the pH over 5.0 after ascorbic acid addition. At this pH, that is higher than the pKa

1

4.25 of ascorbic acid, a hydroxyl radical generating redox cycling reaction involving the mono-anion of vitamin C and copper could take place. The ascorbic acid induced hydroxyl radical generating reaction could easily be mimicked in Milli-Q water by supplementing the water with copper and bicarbonate. Our results demonstrate that ascorbic acid can induce a pH dependent hydroxyl radical generating reaction in copper contaminated household tap water that is buffered with bicarbonate. The impact of consuming ascorbic acid together with copper and bicarbonate containing drinking water on human health is discussed.     

Rapid scavenging of peroxynitrous acid by monohydroascorbate

The reaction of peroxynitrous acid with monohydroascorbate, over the concentration range of 250 μM to 50 mM of monohydroascorbate at pH 5.8 and at 25°C, was reinvestigated and the rate constant of the reaction found to be much higher than reported earlier (Bartlett, D.; Church, D. F.; Bounds, P. L.; Koppenol, W. H. The kinetics of oxidation of L-ascorbic acid by peroxynitrite. Free Radic. Biol. Med. 18:85–92; 1995; Squadrito, G. L.; Jin, X.; Pryor, W. A. Stopped-flow kinetics of the reaction of ascorbic acid with peroxynitrite. Arch. Biochem. Biophys. 322:53–59; 1995). The new rate constants at pH 5.8 are k₁ = 1 × 10⁶ M⁻¹ s⁻¹ and k₋₁ = 500 s⁻¹ for 25°C and k₁ = 1.5 × 10⁶ M⁻¹ s⁻¹ and k₋₁ = 1 × 10³ s⁻¹ for 37°C. These values indicate that even at low monohydroascorbate concentrations most of peroxynitrous acid forms an adduct with this antioxidant. The mechanism of the reaction involves formation of an intermediate, which decays to a second intermediate with an absorption maximum at 345 nm. At low monohydroascorbate concentrations, the second intermediate decays to nitrate and monohydroascorbate, while at monohydroascorbate concentrations greater than 4 mM, this second intermediate reacts with a second monohydroascorbate to form nitrite, dehydroascorbate, and monohydroascorbate. EPR experiments indicate that the yield of the ascorbyl radical is 0.24% relative to the initial peroxynitrous acid concentration, and that this small amount of ascorbyl radicals is formed concomitantly with the decrease of the absorption at 345 nm. Thus, the ascorbyl radical is not a primary reaction product. Under the conditions of these experiments, no homolysis of peroxynitrous acid to nitrogen dioxide and hydroxyl radical was observed. Aside from monohydroascorbate's ability to “repair” oxidatively modified biomolecules, it may play a role as scavenger of peroxynitrous acid.     

CO2.- radical induced cleavage of disulfide bonds in proteins. A gamma-ray and pulse radiolysis mechanistic investigation

Disulfide bond reduction by the CO2.- radical was investigated in aponeocarzinostatin, aporiboflavin-binding protein, and bovine immunoglobulin. Protein-bound cysteine free thiols were formed under gamma-ray irradiation in the course of a pH-dependent and protein concentration dependent chain reaction. The chain efficiency increased upon acidification of the medium, with an apparent pKa around 5, and decreased abruptly below pH 3.6. It decreased also at neutral pH as cysteine accumulated. From pulse radiolysis analysis, CO2.- proved able to induce rapid one-electron oxidation of thiols and of tyrosine phenolic groups in addition to one-electron donation to exposed disulfide bonds. The bulk rate constant of CO2.- uptake by the native proteins was 5- to 10-fold faster at pH 3 than at pH 8, and the protonated form of the disulfide radical anion, [symbol: see text], appeared to be the major protein radical species formed under acidic conditions. The main decay path of [symbol: see text] consisted of the rapid formation of a thiyl radical intermediate [symbol: see text] in equilibrium with the closed, cyclic form. The thiyl radical was subsequently reduced to the sulfhydryl level [symbol: see text] on reaction with formate, generating 1 mol of the CO2.- radical, thus propagating the chain reaction. The disulfide radical anion [symbol: see text] at pH 8 decayed through competing intramolecular and/or intermolecular routes including disproportionation, protein-protein cross-linking, electron transfer with tyrosine residues, and reaction with sulfhydryl groups in prereduced systems. Disproportionation and cross-linking were observed with the riboflavin-binding protein solely. Formation of the disulfide radical cation [symbol: see text], phenoxyl radical Tyr-O. disproportionation, and phenoxyl radical induced oxidation of preformed thiol groups should also be taken into consideration to explain the fate of the oxygen-centered phenoxyl radical.     

Antioxidant and free radical scavenging activities of an exopolysaccharide from a probiotic bacterium

Probiotic bacteria synthesize extracellular polysaccharides (EPSs) with commercially significant physiological and therapeutic activities. This important class of biomolecules is also characterized by their ability to remove reactive oxygen species (ROS) that are formed in the intestine by various metabolic reactions; hence, they exhibit antioxidant activities. Our probiotic bacterium, Bacillus coagulans RK-02, produces an EPS during the exponential and stationary growth phases when grown in a glucose mineral salts medium. The time course of EPS synthesis was studied with respect to biomass growth. The antioxidant and free radical scavenging potential of isolated EPS were studied by various methods, including the beta-carotene-linoleic acid model system, a superoxide radical scavenging assay using the PMS-NADH-nitroblue tetrazolium system, the 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, a hydroxyl radical scavenging assay using the ascorbic acid-Cu(2+)-cytochrome c system and an in vitro microsome peroxidation inhibition study using a thiobarbituric acid assay. The antioxidant activities were compared to known antioxidants vitamin C and E, which were used as reference standards. The results showed that the EPS, which is a heteropolymer composed of four monosaccharides, produced by B. coagulans RK-02 had significant antioxidant and free radical scavenging activities.     

Metabolic bases for differences in sensitivity of two pea cultivars to sulfur dioxide

An oxidative chain reaction of sulfite initiated by the superoxide ion produced in the Mehler reaction has been implicated in the damage of plants exposed to sulfur dioxide. The toxicity of SO₂ may be alleviated by free radical scavenging systems acting to terminate this chain reaction. Hence, the relative sensitivity of plants to SO₂ toxicity could depend on differences in the responses of the levels of antioxidant metabolites and enzymes. The effect of SO₂ exposure on glutathione and ascorbic acid contents, glutathione reductase, and superoxide dismutase activities was assayed in two cultivars (Progress, Nugget) of pea (Pisum sativum L.) in which apparent photosynthesis showed a differential sensitivity to 0.8 microliter per liter SO₂ (R. Alscher, J. L. Bower, W. Zipfel [1987] J Exp Bot 38:99-108). Total and reduced glutathione increased more rapidly and to a greater extent in the insensitive Progress than in the sensitive Nugget, as did glutathione reductase activities. Superoxide dismutase activities increased significantly in Progress, whereas no such change was observed in Nugget as a result of SO₂ exposure. This increase in superoxide dismutase activity was observed at 210 minutes after 0.8 microliter per liter SO₂ concentration had been reached, in marked contrast to the increases in reduced glutathione content and glutathione reductase activity, which were apparent at the 90 minute time point. These data suggest that one basis for the relative insensitivity of the apparent photosynthesis of the pea cultivar Progress to SO₂ is the enhanced response of glutathione reductase, superoxide dismutase activities, and glutathione content.     

Homogentisic acid autoxidation and oxygen radical generation: implications for the etiology of alkaptonuric arthritis

The metabolic disorder, alkaptonuria, is distinguished by elevated serum levels of 2,5-dihydroxyphenylacetic acid (homogentisic acid), pigmentation of cartilage and connective tissue and, ultimately, the development of inflammatory arthritis. Oxygen radical generation during homogentisic acid autoxidation was characterized in vitro to assess the likelihood that oxygen radicals act as molecular agents of alkaptonuric arthritis in vivo. For homogentisic acid autoxidized at physiological pH and above, yielding superoxide (O2-)2 and hydrogen peroxide (H2O2), the homogentisic acid autoxidation rate was oxygen dependent, proportional to homogentisic acid concentration, temperature dependent and pH dependent. Formation of the oxidized product, benzoquinoneacetic acid was inhibited by the reducing agents, NADH, reduced glutathione, and ascorbic acid and accelerated by SOD and manganese-pyrophosphate. Manganese stimulated autoxidation was suppressed by diethylenetriaminepentaacetic acid (DTPA). Homogentisic acid autoxidation stimulated a rapid cooxidation of ascorbic acid at pH 7.45. Hydrogen peroxide was among the products of cooxidation. The combination of homogentisic acid and Fe3+-EDTA stimulated hydroxyl radical (OH.) formation estimated by salicylate hydroxylation. Ferric iron was required for the reaction and Fe3+-EDTA was a better catalyst than either free Fe3+ or Fe3+-DTPA. SOD accelerated OH. production by homogentisic acid as did H2O2, and catalase reversed much of the stimulation by SOD. Catalase alone, and the hydroxyl radical scavengers, thiourea and sodium formate, suppressed salicylate hydroxylation. Homogentisic acid and Fe3+-EDTA also stimulated the degradation of hyaluronic acid, the chief viscous element of synovial fluid. Hyaluronic acid depolymerization was time dependent and proportional to the homogentisic acid concentration up to 100 microM. The level of degradation observed was comparable to that obtained with ascorbic acid at equivalent concentrations. The hydroxyl radical was an active intermediate in depolymerization. Thus, catalase and the hydroxyl radical scavengers, thiourea and dimethyl sulfoxide, almost completely suppressed the depolymerization reaction. The ability of homogentisic acid to generate O2-, H2O2 and OH. through autoxidation and the degradation of hyaluronic acid by homogentisic acid-mediated by OH. production suggests that oxygen radicals play a significant role in the etiology of alkaptonuric arthritis.     

紫色红曲霉对沙棘青稞复合酵素性能的影响研究

【目的】为了对比分析紫色红曲霉是否对沙棘青稞酵素具有促进作用。【方法】以对照组、沙棘组、沙青组、沙青红曲组4种发酵液为研究对象,对其pH、总糖、总酸、可溶性固形物、总酚、总黄酮、抗坏血酸和洛伐他汀、超氧化物歧化酶、脂肪酶和蛋白酶含量、1,1-二苯基-2-苦苯肼自由基清除能力、2,2ʹ-联氮双(3-乙基苯并噻唑啉-6-磺酸)阳离子自由基清除能力、酵母菌活菌数和乳酸菌活菌数进行比较分析。【结果】沙青红曲组的总酚、总黄酮、抗坏血酸和洛伐他汀、超氧化物歧化酶、脂肪酶和蛋白酶含量、1,1-二苯基-2-苦苯肼自由基清除率、2,2ʹ-联氮双(3-乙基苯并噻唑啉-6-磺酸)阳离子自由基清除率、酵母菌活菌数和乳酸菌活菌数均显著高于沙棘组和沙青组(P<0.05)。【结论】该研究证明了紫色红曲霉的添加可提高酵素的性能,对酵素行业的多元化发展有潜在的促进作用。