1-Hydroxy monocyclic carotenoid 3,4-dehydrogenase from a marine bacterium that produces myxol

A crtD (1-HO carotenoid 3,4-dehydrogenase gene) homolog from marine bacterium strain P99-3 included in the gene cluster for the biosynthesis of myxol (3^′,4^′-didehydro-1^′,2^′-dihydro-β,ψ-carotene-3,1^′,2^′-triol) was functionally identified. The P99-3 CrtD was phylogenetically distant from the other CrtDs. A catalytic feature was its high activity for the monocyclic carotenoid conversion: 1^′-HO-torulene (3^′,4^′-didehydro-1^′,2^′-dihydro-β,ψ-caroten-1^′-ol) was prominently formed from 1^′-HO-γ-carotene (1^′,2^′-dihydro-β,ψ-caroten-1^′-ol) in Escherichia coli with P99-3 CrtD, indicating that this enzyme has been highly adapted to myxol biosynthesis. This unique type of crtD is a valuable tool for obtaining 1^′-HO-3^′,4^′-didehydro monocyclic carotenoids in a heterologous carotenoid production system.     

Angiotensin II and angiotensin-(1-7) inhibit the inner cortex Na+ -ATPase activity through AT2 receptor

In the present paper, the modulation of the basolateral membrane (BLM) Na⁺-ATPase activity of inner cortex from pig kidney by angiotensin II (Ang II) and angiotensin-(1–7) (Ang-(1–7)) was evaluated. Ang II and Ang-(1–7) inhibit the Na⁺-ATPase activity in a dose-dependent manner (from 10⁻¹¹ to 10⁻⁵ M), with maximal effect obtained at 10⁻⁷ M for both peptides. Pharmacological evidences demonstrate that the inhibitory effects of Ang II and Ang-(1–7) are mediated by AT₂ receptor: The effect of both polypeptides is completely reversed by 10⁻⁸ M PD 123319, a selective AT₂ receptor antagonist, but is not affected by either (10⁻¹²–10⁻⁵ M) losartan or (10⁻¹⁰–10⁻⁷ M) A779, selective antagonists for AT₁ and AT_(1–7) receptors, respectively. The following results suggest that a PTX-insensitive, cholera toxin (CTX)-sensitive G protein/adenosine 3′,5′-cyclic monophosphate (cAMP)/PKA pathway is involved in this process: (1) the inhibitory effect of both peptides is completely reversed by 10⁻⁹ M guanosine 5′-O-(2-thiodiphosphate) (GDPβS; an inhibitor of the G protein activity), and mimicked by 10⁻¹⁰ M guanosine 5′-O-(3-thiotriphosphate) (GTPγS; an activator of the G protein activity); (2) the effects of both peptides are mimicked by CTX but are not affected by PTX; (3) Western blot analysis reveals the presence of the G_s protein in the isolated basolateral membrane fraction; (4) (10⁻¹⁰–10⁻⁶ M) cAMP has a similar and non-additive effect to Ang II and Ang-(1–7); (5) PKA inhibitory peptide abolishes the effects of Ang II and Ang-(1–7); and (6) both angiotensins stimulate PKA activity.     

Nitric oxide stimulates prostaglandin synthesis in cultured rabbit gastric cells

Both prostaglandins (PGs) and nitric oxide (NO) have cytoprotective and hyperemic effects in the stomach. However, the effect of NO on PG synthesis in gastric mucosal cells is unclear. We examined whether sodium nitroprusside (SNP), a releaser of NO, stimulates PG synthesis in cultured rabbit gastric mucus-producing cells. These cells did not release NO themselves. Co-incubation with SNP (2 × 10⁻⁴, 5 × 10⁻⁴, 10⁻³ M) increased PGE₂ synthesis, and SNP (10⁻³ M) increased PGI₂ synthesis in these cells. Hemoglobin, a scavenger of NO, (10⁻⁵ M) eliminated the increase in PGE₂ synthesis by SNP, but methylene blue, an inhibitor of soluble guanylate cyclase, (5 × 10⁻⁵ M) did not affect the increase in PGE₂ synthesis by SNP. 8-bromo guanosine 3′ : 5′-cyclic monophosphate (8-bromo cGMP), a cGMP analogue, (10⁻⁶, 10⁻⁵, 10⁻⁴, 10⁻³ M) did not affect PGE₂ synthesis. These findings suggest that NO increased PGE₂ and PGI₂ synthesis via a cGMP-independent pathway in cultured rabbit gastric cells.     

贮藏温度对玫瑰鲜花抗氧化能力的影响

新鲜玫瑰花经25℃和4℃贮藏后发现,其花瓣粗提液对DPPH·、.OH的清除能力以及花瓣中多酚和黄酮含量在贮藏3d或4d内上升、随后开始下降;对O₂^·的清除能力以及Vc含量的变化呈持续上升趋势。相关分析表明,花瓣粗提液对DPPH·的清除活性与花瓣多酚含量变化呈显著正相关,对O₂^·的清除活性与花瓣Vc含量变化亦存在显著正相关。4℃贮藏更有利于保持玫瑰花的抗氧化活性。     

Stability of chromatophores during ATP regeneration in an enzyme reactor

ATP regeneration from ADP and inorganic phosphate catalysed by chromatophores from Rhodo-spirillum rubrum has been coupled to the production of glucose-6-phosphate from glucose catalysed by hexokinase. Different ADP derivatives were tested in respect of their function as substrates for the chromatophores, but only 3′NH₂-ADP was phosphorylated. Several factors causing inactivation of the chromatophores during operational conditions were studied. The addition of radical scavengers resulted in an increased stability of the chromatophores, and it was concluded that free radicals had been formed in the presence of oxygen and caused damage to the membranes. In the presence of catalase, a stable ATP production was obtained for 6 h at an activity of 4.5 mol ATP × (mol bacteriochlorophyll)⁻¹ min⁻¹. In a nitrogen flushed reaction medium, the optimum concentration of the redox buffering ascorbic acid changed during the course of several hours of illumination, while it did not change in an air atmosphere.     

Thermodynamics of the disproportionation of adenosine 5'-diphosphate to adenosine 5'-triphosphate and adenosine 5'-monophosphate, II. Experimental data

High-pressure liquid-chromatography and microcalorimetry have been used to determine equilibrium constants and enthalpies of reaction for the disproportionation reaction of adenosine 5′-diphosphate (ADP) to adenosine 5′-triphosphate (ATP) andadenosine 5′-monophosphate (AMP). Adenylate kinase was used to catalyze this reaction. The measurements were carried out over the temperature range 286 to 311 K, at ionic strengths varying from 0.06 to 0.33 mol kg⁻¹, over the pH range 6.04 to 8.87, and over the pMg range 2.22 to 7.16, where pMg = -log a(Mg²⁺). The equilibrium model developed by Goldberg and Tewari (see the previous paper in this issue) was used for the analysis of the measurements. Thus, for the reference reaction: 2 ADp³⁻ (ao) AMp²⁻ (ao)+ ATp⁻ (ao), K° = 0.225 ± 0.010, ΔG° = 3.70 +- 0.11 kJ mol ⁻¹, ΔH° = −1.5 ± 1. 5 kJ mol ⁻¹, °S ° = −17 ± 5 J mol⁻¹ K⁻¹, and ACP_p°≈ = −46 J mo1l⁻¹ K⁻¹ at 298.15 K and 0.1 MPa. These results and the thermodynamic parameters for the auxiliary equilibria in solution have been used to model the thermodynamics of the disproportionation reaction over a wide range of temperature, pH, ionic strength, and magnesium ion morality. Under approximately physiological conditions (311.15 K, pH 6.94, [Mg²⁺] = 1.35 × 10⁻³ mol kg⁻¹, and I = 0.23 mol kg⁻¹) the apparent equilibrium constant (K_A′ = m(ΣAMP)m(ΣATP)/[ m(ΣADP)]²) for the overall disproportionation reaction is equal to 0.93 ± 0.02. Thermodynamic data on the disproportionation reaction and literature values for this apparent equilibrium constant in human red blood cells are used to calculate a morality of 1.94 × 10⁻⁴ mol kg⁻¹ for free magnesium ion in human red blood cells. The results are also discussed in relation to thermochemical cycles and compared with data on the hydrolysis of the guanosine phosphates.     

A performance comparison of choline biosensors: anodic or cathodic detections of H2O2 generated by enzyme immobilized on a conducting polymer

Amperometric choline biosensors were fabricated by the covalent immobilization of an enzyme of choline oxidase (ChO) and a bi-enzyme of ChO/horseradish peroxidase (ChO/HRP) onto poly-5,2′:5′,2″-terthiophene-3′-carboxylic acid (poly-TTCA) modified electrodes (CPMEs). A sensor modified with ChO utilized the oxidation process of enzymatically generated H₂O₂ in a choline solution at +0.6 V. The other one modified with ChO/HRP utilized the reduction process of H₂O₂ in a choline solution at −0.2 V. Experimental parameters affecting the sensitivity of sensors, such as pH, applied potential, and temperature were optimized. A performance comparison of two sensors showed that one based on ChO/HRP/CPME had a linear range from 1.0×10⁻⁶ to 8.0×10⁻⁵ M and the other based on ChO/CPME from 1.0×10⁻⁶ to 5.0×10⁻⁵ M. The detection limits for choline employing ChO/HRP/CPME and ChO/CPME were determined to be about 1.0×10⁻⁷ and 4.0×10⁻⁷ M, respectively. The response time of sensors was less than 5 s. Sensors showed good selectivity to interfering species. The long-term storage stability of the sensor based on ChO/HRP/CPME was longer than that based on ChO/CPME.     

Evaluation of chromosome painting to assess the induction and persistence of chromosome aberrations in bone marrow cells of mice treated with benzene

Intact pZ189 DNA was allowed to replicate in FL-FEN-1⁻ cell line that was established in this laboratory in which the expression of FEN-1 gene was blocked by dexamethasone-inducible expression of antisense RNA to FEN-1. E. coli MBM7070 was transfected with the replicated plasmid, and those with mutations in the supF gene were identified. The frequency of mutants that did not contain recognizable changes in the electrophoretic mobility of the plasmid DNA was scored. The frequency of such mutants was 19.1 × 10⁻⁴ (34/17781), significantly higher than those of 2.9 × 10⁻⁴ (4/13668) and 3.0 × 10⁻⁴ (3/9857) in the corresponding controls, respectively. Sequence analysis of the supF genes of these mutants showed that all (37/37) the base substitutions occurred at C:G base pairs; 68% (23/37) of the base substitutions were base transversions, while 32% (12/37) were transitions. Approximately 76% (23/37) of these base substitutions occurred frequently at nine positions; two of these sites contain triple pyrimidine (T or C) repeat upstream to the mutated base; four of these sites consist of 5′-TTN₁N₂ and mutations occurred at N₁ site sequence; another two sites have the characteristics of triple A flanked at both 5′ and 3′ side by TCT, with the base substitution occurring at C in the context sequence. These data suggested that these sites are the hot spot of mutagenesis in plasmid replicated in FEN-1-deficient cells. Besides the mutator phenotype of the FEN-1-deficient cell, it was also demonstrated that FEN-1-deficient cell exhibited an increased N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) sensitive phenotype.     

Relationships between structures of hydroxyflavones and their antioxidative effects

Even hydroxyflavones show diverse biological functions, they have two common features such as showing antioxidative effects and containing hydroxyl groups. The authors tested the antioxidative effects of thirty hydroxyflavones using 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay. While the scavenging activity of galangin, 3,5,7-trihydroxyflavone was 52.5%, fisetin, 3,7,3′,4′-tetrahydroxyflavone showed 85.2%. To investigate the relationships between the structures of hydroxyflavones and their antioxidative effects, the three-dimensional quantitative structure–activity relationships were examined.     

Cytochrome c interaction with the mitochondrial membrane: A spin label study

Horse-heart ferrocytochrome c has been labeled with N-(2,2,5,5-tetramethyl-3-pyrrolidinyl-1-oxyl) iodoacetamide at methionine-65. The paramagnetic resonance spectrum of labeled ferricytochrome c indicates a weak immobilization of the radical (τ_c = 9.3·10⁻¹⁰ sec) which becomes stronger upon binding of labeled cytochrome c to cytochrome c-depleted mitochondrial membranes (τ_c = 3.3·10⁻⁹ sec). The hyperfine coupling constant remains, however, unchanged (16.7 ± 0.1 gauss) indicating that the cytochrome c binding site is highly polar. The region where cytochrome c is bound to the membrane is insensitive to large variations of medium viscosity.     

Synthesis of graft copolymer (k-carrageenan-g-N,N-dimethylacrylamide) and studies of metal ion uptake, swelling capacity and flocculation properties

Graft copolymer of k-carrageenan and N,N-dimethylacrylamide has been synthesized by free radical polymerization using peroxymonosulphate/glycolic acid redox pair in an inert atmosphere. The grafting parameters i.e. grafting ratio, add on and efficiency decrease with increase in concentration of k-carrageenan from 0.6 to 1.4 g dm⁻³ and hydrogen ion from 3 × 10⁻³ to 7 × 10⁻³ mol dm⁻³, but these grafting parameters increase with increase in concentration of N,N-dimethylacrylamide from 16 × 10⁻² to 32 × 10⁻² mol dm⁻³, and peroxymonosulphate from 0.8 × 10⁻² to 2.4 × 10⁻² mol dm⁻³. The metal ion sorption, swelling behaviour and flocculation properties have been studied. The intrinsic viscosity of pure and grafted samples has been measured by using Ubbelohde capillary viscometer. Flocculation capability of k-carrageenan and k-carrageenan-g-N,N-dimethylacrylamide for both coking and non-coking coals has been studied for the treatment of coal mine waste water. The graft copolymer has been characterized by Infrared (IR) spectroscopy and thermogravimetric analysis.     

Effects of peptide YY and its analogues on chloride ion secretion in fed and fasted rat jejunum

The aim of our study was to determine whether a meal modifies the antisecretory response induced by PYY and the structural requirements to elicit antisecretory effects of analogue PYY(22–36) for potential antidiarrhea therapy. The variations in short-circuit current (Isc) due to the modification of ionic transport across the rat intestine were assessed in vitro, using Ussing chambers. In fasted rats, PYY induced a dose- and time-dependent reduction in Isc, with a sensitivity threshold at 5 × 10⁻¹¹ M (ΔIsc −2 ± 0.5 μA/cm²). The reduction was maximal at 10⁻⁷ M (Isc −23 ± 2 μA/cm²), and the concentration producing half-maximal inhibition was 10⁻⁹ M. At 10⁻⁷ M, reduction of Isc by PYY reached 90% of response to 5 × 10⁻⁵ M bumetanide. The PYY effect was partly reversed by 10⁻⁵ M forskolin (Isc +13.43 ± 2.91 μA/h·cm², p < 0.05) or 10⁻³ M dibutyryl adenosine 3′,5′ cyclic monophosphate (Isc +12 ± 1.69 μA/cm², p < 0.05). Naloxone and tetrodotoxin did not alter the effect of PYY. In addition, PYY and its analogue P915 reduced net chloride ion secretion to 2.85 and 2.29 μEq/cm² (p < 0.05), respectively. The antisecretory effect of PYY was accompanied by dose- and time-dependent desensitization when jejunum was prestimulated by a lower dose of peptide. The antisecretory potencies exhibited by PYY analogues required both a C-terminal fragment (22–36) and an aromatic amino acid residue (Trp or Phe) at position 27. At 10⁻⁷ M the biological activity of PYY was lower in fed than fasted rats (p < 0.001). Our results confirm the antisecretory effect of PYY, but show that the fed period is accompanied by desensitization, similar to the transient desensitization observed in the fasted period with cumulative doses. This suggests that PYY may act as a physiological mediator that reduces intestinal secretion.     

Nitrogen, sulfur and oxygen donor adducts with copper(II) complexes of antitumor 2-formylpyridinethiosemicarbazone analogs: Physicochemical and cytotoxic studies

The preparation of N-, S- and O-donor ligand adducts with CuX⁺(HX=6-methyl-2-formylpyridinethiosemicarbazone (6HL); 2-formylpyridine-2^′-methylthiosemicarbazone (2′L); 2-formylpyridine-4′-methylthiosemicarbazone (4′HL)) is described. The N-donors, 2,2′-bipyridyl (bipy), 4-dimethylaminopyridine (dmap) give the complexes [Cu(6L)(bipy)]PF₆, [Cu(6L)(bipy)]Cl·5H₂O, [Cu(4′L)(bipy)]PF₆, [Cu(6L)(dmap)₂]PF₆·2.5 H₂O and [Cu(4′L)(dmap)₂]PF₆·H₂O which have been characterized by physical and spectroscopic techniques. Pentafluorothiophenolate (pftp) gives S-donor complexes [CuX(pftp)] (X=6L and 4′L) and thiolato co-ordination is proposed on the basis of spectroscopic evidence. Paratritylphenolate (ptp) and HPO²⁻₄ give O-donor complexes [Cu(6L)(ptp)], [Cu(4′L)(ptp)], [{Cu(6L)}₂HPO₄]·4H₂O, and [{Cu(4^′L)}₂HPO₄]·5H₂O which have been characterized by physical and spectroscopic techniques, as have the precursor complexes [Cu(6L)(CH₃COO)]·H₂O, [Cu(4′L)(CH₃COO)], Cu(6HL)(CF₃COO)](CF₃COO)·0.5H₂O, [Cu(4′HL)(CF₃COO)](CF₃COO), [Cu(2′L)Cl₂] and [Cu(2′L)(NO₃)₂]. Protonation constants for the ligands and some of their complexes have been determined. 2-Formylpyridinethiosemicarbazone (HL) complexes of silver, gold, zinc, mercury, cadmium and lead are also discussed. Cytotoxicity against the human tumor cell line HCT-8 and antiviral data for selected compounds are presented.     

Spectrophotometric and kinetic studies of the binding of Ni, Co, and Mg to poly(dG-dC) · poly(dG-dC). Determination of the stoichiometry of the Ni-induced B → Z transition

Data are reported for the binding of Ni²⁺, Co²⁺, and Mg²⁺ to the B-form of double-stranded poly(dG-dC) at ionic strength conditions I = 0.001 M, 0.01 M, and 0.1 M. The apparent binding constants for Ni²⁺ and Co²⁺ are about the same and are 2- to 3-fold higher than those for Mg²⁺. Kinetic studies indicate that Mg²⁺ binds to the polynucleotide mainly (or solely) as a mobile cloud (electrostatically, outer-sphere), whereas the transition metal ions undergo site binding (inner-sphere coordination) with poly(dG-dC). The kinetic data suggest that an Ni²⁺ ion coordinates to more than one binding site at the polynucleotide, presumably to G-N₇ and a phosphate group.

At low ionic strength conditions the addition of Ni²⁺ induces a B → Z conformational transition in poly(dG-dC). As demonstrated by UV absorption and CD spectroscopy, the transition occurs at I = 0.001 M already when 3 × 10⁻⁵ – 7 × 10⁻⁵ M of Ni²⁺ are added to 8 × 10⁻⁵ M (in monomeric units) of poly(dG-dC), and at I = 0.01 M between 2.5 × 10⁻⁴ and 4.5 × 10⁻⁴ M of Ni²⁺. Using murexide as an indicator of the concentration of free Ni²⁺ ions, the amount of Ni²⁺ which is bound to the polynucleotide could be determined. At I = 0.001 M it was established that the B → Z transition begins when 1 Ni²⁺ is bound coordinatively per four base pairs, and the transition is complete when 1 Ni²⁺ is bound coordinatively per three base pairs. It is this coordinated Ni²⁺ which induces the B → Z transition.     

Effect of O6-alkylguanine-DNA alkyltransferase on the frequency and spectrum of mutations induced by N-methyl-N''-nitro-N-nitrosoguanidine in the HPRT gene of diploid human fibroblasts

N-Methyl-N′-nitro-N-nitrosoguanidine (MNNG) reacts with 12 nucleophilic sites in DNA to induce a variety of lesions, but O⁶-methylguanine (O⁶-MeG) and O⁴-methylthymine are the most effective premutagenic lesions produced, mispairing with thymine and guanine, respectively. O⁶-MeG is repaired by O⁶-alkylguanine-DNA alkyltransferase (AGT), which removes the methyl group from the O⁶ position and transfers it to itself, rendering the transferase inactive. When diploid human fibroblasts were exposed to 25 μM, O⁶-benzylguanine (O⁶-BzG) in the medium for 3 h, their level of AGT activity was dramatically reduced, to a level of at most 1.6% of the control. Populations of cells pretreated with this level of O⁶-BzG for 2 h or not pretreated, were exposed to MNNG at a concentration of 2, 4 or 6 μM in the presence or absence of O⁶-BzG and assayed for survival of colony-forming ability and the frequency of 6-thioguanine-resistant cells (mutations induced in the HPRT gene). O⁶-BzG (25 μM) was also present in the appropriate half of the cells during the 24 h immediately follwing exposure to MNNG. This 27-h exposure to O⁶-BzG alone had no cytotoxic or mutagenic effect on the cells but significantly increased the cytotoxicity and mutagenecity of MNNG, increasing the mutant frequency to that found previously in human cells constitutively devoid of AGT activity. At doses of 2 μM and 4 μM MNNG, the mutant frequency observed with the AGT-depleted cells was 120 × 10⁻⁶ and 240 × 10⁻⁶, respectively; in the cells with abundant AGT activity, these values were 10 × 10⁻⁶ and 20 × 10⁻⁶, respectively. DNA-sequence analysis of the coding region of the HPRT gene in 36 independent mutants obtained from MNNG-treated AGT-depleted populations and 36 from the control populations showed that even though AGT repair lowered the frequency of mutants by more than 90%, it did not affect the kinds of mutations induced by MNNG nor the strand distribution of the premutagenic guanine lesions. In mutants from the AGT-depleted cells, there were 26 base substitutions and 13 putative splice site mutations; in the control, there were 25 base substitutions and 11 splice site mutations. All but two substitutions involved G · C with 92% being G · C → A · T. In both sets, of the premutagenic lesions were located in the nontranscribed strand. Many ‘hot spots’ were seen, and there was evidence that AGT repaired more lesions from the 5′ half of the gene than from the 3′ half.     

Supported bilayer lipid membranes modified with a phosphate ionophore

This article reports the electrical responses of a phosphate ionophore, the cyclic polyamine 3-decyl-1,5,8-triazacyclodecane-2,4-dione (N₃-cyclic amine) incorporated into metal supported bilayer lipid membranes (s-BLM). Teflon coated silver wire was used as a support. In a potentiometric mode, the ionophore had a response that was linearly related to the logarithm of HPO₄²⁻ concentration and was also dependant on pH. Selectivity coefficients for other anions compared to HPO₄²⁻ ions, determined by the separate solution method, fell within the range 1.73 × 10⁻⁴ to 6.38 × 10⁻².     

4-Mercaptoimidazoles derived from the naturally occurring antioxidant ovothiols 1. Antioxidant properties

4-Mercaptoimidazoles derived from the naturally occurring family of antioxidants, the ovothiols, were assayed for their antioxidant properties. These compounds are powerful HOCI scavengers, more potent than the aliphatic thiol N-acetylcysteine. They react slowly with hydrogen peroxide with second order rate constants of 0.13-0.89 M^-1 s^-1. Scavenging of hydroxyl radical occurs at a diffusion-controlled rate (k = 2.0-5.0 × 10¹⁰ M^-1 s^-1) for the most active compounds, which are also able to inhibit copper-induced LDL peroxidation. The combination of radical scavenging and copper chelating properties may explain the inhibitory effects on LDL peroxidation. Two molecules of mercaptoimidazole can chelate a copper ion and form a square planar complex detected by EPR. Compounds bearing an electron-withdrawing group on position 2 of the imidazole ring are the most potent antioxidant molecules in this series.     

Clarification of the Relationship Between Free Radical Spin Trapping and Carbon Tetrachloride Metabolism in Microsomal Systems

It has been proposed that the C-phenyl-N-tert-butylnitrone/trichloromethyl radical adduct (PBN/^•CCl₃) is metabolized to either the C-phenyl-N-tert-butylnitrone/carbon dioxide anion radical adduct (PBN/^•CO₂⁻) or the glutathione (GSH) and CCl₄-dependent PBN radical adduct (PBN/[GSH-^•CCl₃]). Inclusion of PBN/^•CCl₃ in microsomal incubations containing GSH, nicotinamide adenine dinucleotide phosphate (NADPH), or GSH plus NADPH produced no electron spin resonance (ESR) spectral data indicative of the formation of either the PBN/[GSH-^•CCl₃] or PBN/^•CO₂⁻ radical adducts. Microsomes alone or with GSH had no effect on the PBN/^•CCl₃ radical adduct. Addition of NADPH to a microsomal system containing PBN/^•CCl₃ presumably reduced the radical adduct to its ESR-silent hydroxylamine because no ESR signal was observed. The Folch extract of this system produced an ESR spectrum that was a composite of two radicals, one of which had hyperfine coupling constants identical to those of PBN/^•CCl₃. We conclude that PBN/^•CCl₃ is not metabolized into either PBN/[GSH-^•CCl₃] or PBN/^•CO₂⁻ in microsomal systems.     

茶多糖的抗氧化活性及对细胞氧化损伤的保护机制

茶多糖是一种从茶叶中提取的酸性糖蛋白,具有良好的抗氧化活性。以自由基清除率为指标,分析皖西南地区夏秋茶多糖的抗氧化活性,基于H₂O₂和EDTA-Fe²⁺建立的外源性羟基自由基(·OH)损伤细胞模型和PMA诱导内源性羟基自由基损伤模型,进一步探讨茶多糖对自由基损伤的修复作用机制。结果表明,茶多糖具有良好的体外抗氧化活性,对DPPH·和·OH均具有较强的清除效果,EC₅₀值分别为209.5和535.2μg·mL^–1,最大清除效率与Vc相当。细胞增殖实验表明,外源性和内源性自由基氧化损伤模型中细胞存活率均随着茶多糖浓度的增加而升高,在茶多糖浓度为800μg·mL^–1时细胞存活率分别高达87.41%和85.84%,且显著高于模型组(47.67%和48.03%)。在修复机制上,利用激光共聚焦显微镜显影细胞内活性氧(ROS)分布以及荧光强度,分析结果显示,与模型组相比,茶多糖对于细胞模型中外源和内源性ROS均具有明显的清除效果,与体外抗氧化实验结果一致。茶多糖在体外表...