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1.
YCT is a semipurified extract from Cratoxylum cochinchinense that has antioxidant properties and contains mostly mangiferin. We show here that YCT is selectively toxic to certain cell types and investigate the mechanisms of this toxicity in Jurkat T cells. By flow cytometric analyses, we show that YCT causes intense oxidative stress and a rise in cytosolic Ca 2+. This is followed by a rise in mitochondrial Ca 2+, release of cytochrome c, collapse of Δψ m, a fall in ATP levels, and eventually cell death. The mechanism(s) of intense oxidative stress may involve a plasma membrane redox system, as cell death is inhibited by potassium ferricyanide. Cell death has some features of apoptosis (propidium iodide staining, externalization of phosphatidylserine, limited caspase-3 and -9 activities), but there was no internucleosomal DNA fragmentation. 相似文献
2.
Relaxation Young's and shear moduli of bovine bone and bone collagen were investigated. It was found that each relaxation process observed had two stages, which were referred to as process I and process II in order of time. Process II was described by a simple exponential decay while process I was not. The Kohlrausch-Williams-Watts (KWW) function, ψ( t) = exp[ t/τ 1) B] (0 < B < 1), was found to be suitable to describe process I. The normalized relaxation modulus, Mr( t), was expressed by the combination of the simple exponential type relaxation function and the KWW function Mr=A1exp[−(t/τ1)B]+A2exp[(t/τ1)](0<B1) On the basis of this equation, the relaxation mechanism in bone and bone collagen was identified. According to the model proposed for the KWW relaxation function, the stress relaxation process in bone was considered to be governed by viscoelastic properties of matrix collagen fiber. The model for the KWW relaxation function requires the disordered glassy structure of collagen fiber, which is consistent with the results of the structural investigations. 相似文献
3.
Cu aq+ forms stable complexes with carbon monoxide in aqueous solutions. Furthermore it reacts very fast with aliphatic radicals. The reaction of Cu(CO) maq+ with methyl radicals, •CH 3 was studied using the pulse-radiolysis technique. The results point out that methyl radicals react with Cu(CO) aq+ to form an unstable intermediate with a Cu II-C σ bond identified as (CO)Cu II-CH 3+, k = (1.1±0.2) × 10 9 M −1 s −1. This intermediate has a strong LMCT charge transfer band (λ max = 385 nm, max = 2500 M −1 cm −1) which is similar to the absorption bands of other transient complexes with Cu II-alkyl σ bonds. The coordinated carbon monoxide in (CO)Cu II-CH 3+ inserts into the copper—carbon bond (or rather the coordinated methyl migrates to the coordinated carbon monoxide ligand) at a rate of (3.0±0.8) × 10 2 s −1 to form the copperacetyl complex (CO) mCu II-C(CH 3)=O + (λ max = 480 nm, max = 2100 M −1 cm −1). The rate of formation of (CO)Cu II-CH 3+ and of the insertion reaction are pH independent. The complex (CO) mCu II-C(CH 3)=O + is also unstable and decomposes heterolytically to yield acetaldehyde and Cu aq2+ as the final stable products. This reaction is slightly pH dependent. The same reactivity pattern has been observed for the Cu(CO naq+ complexes ( n = 2 or 3). The results clearly point out that CO remains coordinated to transient complexes of the type Cu II-alkyl. 相似文献
4.
Microbial growth in multisubstrate environments is posed as a problem of multivariable constraint optimization. The optimization aims at maximizing the instantaneous growth rate of cells. The model developed for microbial growth using this hypothesis involves simple representation of complex cell structure as an optimization function which regulates the interplay of cellular machinery. The model parameters are estimated using single substrate growth data. Model simulation fits very well with earlier published experimental data of bacterial growth of Klensiella oxytoca on a variety of sugar mixtures involving glucose, fructose, lactose, and xylose. Moreover, the model is also able to predict the diauxic growth of Saccharomyces cerevisiae on glucose and galactose. One of the interesting outcomes of the above representation is the ability to prove analytically that the growth on the mixture of two sugars will be diauxic if one of the substrates has a very low Ks value and a high μ m value. 相似文献
5.
The viscosity in the low shear rate Newtonian domain of three biopolymers, locust bean gum, guar gum and xanthan gum was studied as a function of temperature and of polymer concentration in various aqueous solvents. The intrinsic viscosities [η] o of both galactomannans are not modified in the presence of 10 or 40% sucrose. In this case, a master curve relating the Newtonian specific viscosity (η sp) o, to the reduced concentration c[η] o is obtained and allows (in good agreement with theoretical conjectures), two critical concentrations C* and C** to be defined, from which the value of the expansion coefficient may be estimated. For xanthan, as expected for a polyelectrolyte, [η] o depends strongly on salt concentration and on added sucrose and the results did not obey the above-mentioned master curve. However, it is shown that (η sp) o depends only on xanthan concentration when C > C**, and then it is assumed that chain dimensions have attained their unperturbed values whatever the solvent. Considering that both types of chains, random coils (galactomannans) and semi-rigid (xanthan) should give the same (η sp) o- C[η] o master curve for C > C** when [η] o is replaced by its unperturbed counterpart [η] θ, a method for estimating [η] θ for the xanthan sample is proposed. In conclusion, the numerous exceptions to the widely accepted (η sp) o vs C[η] o “universal” behaviour are mainly ascribed to significant differences in expansion coefficient values which depend on both the polymer and the solvent. 相似文献
6.
Nitric oxide (NO), a potent vasodilator, plays a pivotal role in blood pressure regulation. Endothelial NO synthase gene ( NOS3) polymorphisms influence NO levels. Here, we investigated the role of the – 922A/G, – 786T/C, 4b/4a, and 894G/T polymorphisms of the NOS3 and NO x levels in 800 consecutive unrelated subjects comprising 455 patients of essential hypertension and 345 controls. The polymorphisms were investigated independently and as haplotypes. Plasma NO x levels (nitrate and nitrite) were estimated by the Griess method. Genotype frequencies for the –786T/C, 4b/4a, and 894G/T polymorphisms differed significantly ( P < 0.001) between patients and controls and were associated with an increased risk of hypertension (OR = 2.0, OR = 3.8, OR = 1.6, respectively). The 4-locus haplotypes ATaG (H1), ATaT (H2), and GCaG (H3) were significantly associated with essential hypertension and served as susceptible haplotypes ( P ≤ 0.0001). On the other hand, haplotypes ATbG (H4) and GTbG (H5) were negatively associated with hypertension and served as protective haplotypes ( P < 0.0001). NO x levels were significantly lower in patients than controls ( P < 0.0001). The individual polymorphisms showed marginal association with NO x level; however, the susceptible haplotype H2 associated significantly with lower NO x levels in patients ( P < 0.001) and conversely the haplotype H4 with higher NO x levels in controls ( P < 0.001). In conclusion, the 4b/4a and likely – 786T/C polymorphisms were identified as the determinants modifying the risk of hypertension. This study identifies the NOS3 variants and haplotypes as genetic risk factors and as useful markers of increased susceptibility to the risk of essential hypertension. 相似文献
7.
OBJECTIVE--To examine the effect on lipid and lipoprotein concentrations when butter or an unsaturated margarine is used for cooking or spreading in a reduced fat diet. DESIGN--Randomised crossover study with two intervention periods of six weeks'' duration separated by a five week washout. SETTING--Community setting in New Zealand. SUBJECTS--49 volunteers with polygenic hypercholesterolaemia and baseline total cholesterol concentration in the range 5.5-7.9 mmol/l. MAIN OUTCOME MEASURES--Concentrations of total and low density lipoprotein, Lp(a) lipoprotein, high density lipoprotein, apolipoprotein B 100, and apolipoprotein A I. RESULTS--Concentrations of low density lipoprotein cholesterol and apolipoprotein B were about 10% lower with margarine than with butter. Lp(a) lipoprotein and high density lipoprotein cholesterol concentrations were similar with the two diets. CONCLUSION--Despite concerns about adverse effects on lipoproteins of trans fatty acids in margarines, the use of unsaturated margarine rather than butter by hypercholesterolaemic people is associated with a lipoprotein profile that would be expected to reduce cardiovascular risk. 相似文献
8.
Evidence is presented suggesting, for the first time, that the protein foldability metric σ = ( Tθ − Tf) / Tθ, where Tθ and Tf are, respectively, the collapse and folding transition temperatures, could be used also to measure the foldability of RNA sequences. These results provide further evidence of similarities between the folding energy landscapes of proteins and RNA. The importance of σ is discussed in the context of the in silico design of rapidly foldable RNA sequences. 相似文献
9.
To study mechanisms of aromatase inhibition in brain cells, a highly effective non-steroidal aromatase inhibitor (Fadrozole; 4-[5,6,7,8-tetra-hydroimidazo-(1,5- a)-pyridin-5-yl] benzonitrile HCl; CGS 16949A) was compared with endogenous C-19 steroids, known to be formed in the preoptic area, which inhibit oestrogen formation. Using a sensitive in vitro tritiated water assay for aromatase activity in avian (dove) preoptic tissue, the order of potency, with testosterone as substrate was: Fadrozole ( Ki < 1 × 10 −9 M) > 4-androstenedione 5-androstanedione > 5-dihydrotestosterone ( Ki = 6 × 10 −8 M) > 5β-androstanedione > 5β-dihydrotestosterone ( Ki = 3.5 × 10 −7 M) > 5-androstane-3, 17β-diol ( Ki = 5 × 10 −6 M) > 5β-androstane-3β,17β-diol. Five other steroids, 5β-androstane-3,17β-diol, 5-androstane-3β,17β-diol, progesterone, oestradiol and oestrone, showed no inhibition at 10 −4 M. The kinetics indicate that endogenous C-19 steroids show similar competitive inhibition of the aromatase as Fadrozole. Mouse (BALB/c) preoptic aromatase was also inhibited by Fadrozole. We conclude that endogenous C-19 metabolites of testosterone are effective inhibitors of the brain aromatase, and suggest that they bind competitively at the same active site as Fadrozole. 相似文献
10.
Androst-4-ene-3,17-dione (androstenedione) was found to be a potent competitive inhibitor of the NADH-supported reduction of retinal in rat hepatic microsomes ( Ki 42 μM, Km/ Ki ratio 1.1). Similarly, the NADH-mediated reduction of androstenedione was inhibited in mixed fashion by retinal ( Ki 12 μM, Km/ Ki ratio 0.34). In subsequent experiments the cofactor NADH exhibited an identical Km (8 μM) in the microsomal reductions of both substrates. Acidic pH markedly stimulated the microsomal reduction of androstenedione to testosterone and was also found to enhance retinal reduction to retinol, although the latter reaction exhibited a district pH optimum between 6.0 and 6.5. These results suggest that a common enzyme may participate in the reduction of both substrates but at least one other enzyme probably participates in hepatic microsomal testosterone production. 相似文献
11.
Implantable prosthetic devices can often affect the recipient's hemostasis, with possible hemolysis and thrombus formation. Since such devices can produce turbulent flow, it is important to characterize it as accurately as possible, by means of the Reynolds stress tensor. Some parameters related to the latter have been often used to provide a quantity related to the possible damage to blood constituents: the TSS max, for instance, has been associated with hemolysis. It can be expressed as TSS max=(σ 1−σ 3)/2, σ 1 and σ 3 being the highest and lowest principal normal stresses (PNSs) in each point of the flow. In the present work, the average value of the shear stress over a spherical surface, representative of a blood component, is derived. All three PNSs (σ1, σ2 and σ3) are found to have an equal role in the determination of this parameter, since the relative formula shows a marked symmetry with respect to the PNSs. The average shear stress level, for a given (σ1, σ3) pair (hence, for a given TSSmax), has a minimum and maximum value, depending on the particular σ2 value yielded by the local structure of the turbulent flow field. A numerical investigation on more complex geometries shows similar results. The role of the intermediate PNS is thus shown for the first time to have a physical relevance. The presented results can be useful whenever a spatial averaging of the shear field is important to be assessed, such as in the case of platelet activation. A new parameter is thus proposed, which can be correlated with prosthetic devices complications. 相似文献
12.
Hydroxylated 2,19-methylene-bridged androstenediones were designed as potential mimics of enzyme oxidized intermediates of androstenedione. These compounds exhibited competitive inhibition with low micromolar affinities for aromatase. These inhibitory constants ( Ki values) were 10 times greater than the 2,19-methylene-bridged androstenedione constant ( Ki = 35–70 nM). However, expansion of the 2,19-carbon bridge to ethylene increased aromatase affinity by 10-fold ( Ki = 2 nM). Substitution pf a methylene group with oxygen and sulfur in this expanded bridge resulted in Ki values of 7 and 20 nM, respectively. When the substituent was an NH group, the apparent inhibitory kinetics changed from competitive to uncompetitive. All of these analogs exhibited time-dependent inhibition of aromatase activity following preincubation of the inhibitor with human placental microsomes prior to measuring residual enzyme activity. Part of this inhibition was NADPH cofactor-dependent for the 2,19-methyleneoxy- but not for the 2,19-ethylene-bridged androstenedione. The time-dependent inhibition for these four analogs was very rapid since they exhibited τ 50 values, the t1/2 for enzyme inhibition at infinite inhibitor concentration, of 1 to 3 min. These A-ring-bridged androstenedione analogs represent a novel series of potent steroidal aromatase inhibitors. The restrained A-ring bridge containing CH 2, O, S, or NH could effectively coordinate with the heme of the P450 aromatase to allow the tight-binding affinities reflected by their nanomolar Ki values. 相似文献
13.
The microsomal fraction from the testes of immature pigs (<1 week old) contains 3β-hydroxysteroid dehydrogenase-isomerase (3β-HSD-isomerase) activities that convert dehydroepiandrosterone (DHA) to 4-androstenedione and 5,16-androstadien-3β-ol (andien-β) to 4,16-androstadien-3-one (dienone). These reactions are necessary for the biosynthesis of hormonally and pheromonally active steroids. Kinetic analyses of these activities were done to determine whether they are catalysed by a single enzyme or if there is any interaction between the substrates and products of one reaction on the activity of the other enzyme. Kinetic parameters were determined and the affinities for steroid substrate were similar (7–9 μmol/l) but the Vmaxapp value for the conversion of andien-β to dienone was 10-fold that of the DHA to 4-androstenedione reaction. In analyses of the conversion of DHA to 4-androstenedione, neither andien-β nor dienone inhibited the reaction and especially, no effect on the Kmapp for DHA was observed which would have indicated competition between DHA and andien-β for the same active site ( Kiapp from slope and intercept replots were between 3 and 80 times the values of the kinetic constants). Similarly, DHA and 4-androstenedione had minor or negligible effects on the conversion of andien-β to dienone ( Kiapp from slope replots were the same as the Kmapp but the Kiapp from the intercept replot was 12 to 25% of the Vmaxapp). It is concluded that substrate specific 3β-HSD-isomerases for andien-β and DHA exist in the immature pig testis and there is little, if any interaction between these enzymes. 相似文献
14.
The method of continuous variation, often known as the Job plot, has long been used for determining the stoichiometry of two interacting components. The correct binding ratio, n, is generally obtained when the total concentration of the reactants, Co, is much greater than the dissociation constants involved. For non-cooperative binding systems, the stoichiometry varies between one and n as Co increases; whereas for positive cooperative systems, values larger than n may be observed at low Co. In this report, we present examples to illustrate how the changing apparent stoichiometries as a function of Co can provide clues for differentiating various binding mechanisms. To test these concepts, we examined the chelation of Fe(II) with ferrozine in the range of Co=7 to 210 μM with Fe(II) expressed in molar concentration or in terms of its binding equivalents (three in this case). The results were analyzed according to several models and found to be most consistent with the mechanism of one-step complex formation or infinite cooperativity with a Kd of 8 μM. 相似文献
15.
Flax pectins, with a low anhydrogalacturonic acid content (AGA≤50%), have been studied by viscometry, light scattering and size exclusion chromatography. After removal of interfering superstructures, intrinsic viscosities were correlated with weight average molecular weights to give a Mark-Houwink coefficient a=0·69. The persistence length of these heterogeneous chains (PI: q=20–25 Å), compared with that of homogalacturonan ones previously studied (PII–PIII: q=67 Å), shows a higher segment density (branched conformation). Using a wide range of experimental data ((η), M i, K d) obtained on narrow pectic fractions of known composition, specific calibration curves of the Sephacryl 200/0·2
NaCl/Flax pectins (PI or PII–PIII) system were established. Applied to the indirect characterization of flax pectins, this size exclusion chromatography (SEC) system constitutes a very convenient method for analysing the molecular and macromolecular parameters ((η), M w, M n, I p, UV) or for controlling the molecular weight distribution of pectins in flax cell walls during the physiological steps of growth and retting. 相似文献
16.
The in vitro metabolism of cortisol in human liver fractions is highly complex and variable. Cytosolic metabolism proceeds predominantly via A-ring reduction (to give 3,5β-tetrahydrocortisol; 3,5β-THF), while microsomal incubations generate upto 7 metabolites, including 6β-hydroxycortisol (6β-OHF), and 6β-hydroxycortisone (6β-OHE), products of the cytochrome P450 (CYP) 3A subfamily. The aim of the present study was, therefore, to examine two of the main enzymes involved in cortisol metabolism, namely, microsomal 6β-hydroxylase and cytosolic 4-ene-reductase. In particular, we wished to assess the substrate specificity of these enzymes and identify compounds with inhibitory potential. Incubations for 30 min containing [ 3H]cortisol, potential inhibitors, microsomal or cytosolic protein (3 mg), and co-factors were followed by radiometric HPLC analysis. The Km value for 6β-OHF and 6β-OHE formation was 15.2 ± 2.1 μM (mean ± SD; n = 4) and the Vmax value 6.43 ± 0.45 pmol/min/mg microsomal protein. The most potent inhibitor of cortisol 6β-hydroxylase was ketoconazole ( Ki = 0.9 ± 0.4 μM; N = 4), followed by gestodene ( Ki = 5.6 ± 0.6 μM) and cyclosporine ( Ki = 6.8 ± 1.4 μM). Both betamethasone and dexamethasone produced some inhibition ( Ki = 31.3 and 54.5 μ, respectively). However, substrates for CYP2C (tolbutamide), CYP2D (quinidine), and CYP1A (theophylline) were essentially non-inhibitory. The Km value for cortisol 4-ene-reductase was 26.5 ± 11.2 μM ( n = 4) and the Vmax value 107.7 ± 46.0 pmol/min/mg cytosolic protein. The most potent inhibitors were androstendione ( Ki = 17.8 ± 3.3 μM) and gestodene ( Ki = 23.8 ± 3.8 μM). Although both compounds have identical A-rings to cortisol, and undergo reduction, inhibition was non-competitive. 相似文献
17.
The purpose of this study was to calculate, as a function of time, segmental contributions to the vertical ground reaction force Fz from positional data for the landing phase in running. In order to evaluate the accuracy of the method, time histories of the sum of the segmental contributions were compared to Fz( t) measured directly by a force plate. The human body was modeled as a system of seven rigid segments. During running the positions of markers defining these segments were monitored using a video analysis system operating at 200 Hz. Special care was taken to minimize marker movement relative to the mass centers of segments, and low-pass cutoff frequencies of 50 Hz (markers defining leg segments) and 15–20 Hz (markers defining upper body) were used in filtering the position time histories so as to ensure that high signal frequencies were preserved. The magnitude of the high-frequency peak in Fz, also known as ‘impact force peak’, was estimated with errors <10%, while the time of occurrence of the peak was estimated with errors <5 ms. It would appear that the positional data were sufficiently accurate to be used for calculation of intersegmental forces and moments during the landing phase in running. Analysis of the segmental contributions to Fz(t) revealed that the first peak in Fz has its origin in the contribution of support leg segments, while its magnitude is determined primarily by the contribution of the rest of the body. These contributions could be varied independently by changing running style. It follows that if the possible relationship between ‘impact force peaks’ and injuries is to be investigated, or if the effects of running shoe and surface construction on these force peaks are to be evaluated, the calculation of segmental contributions to Fz(t) is a more suitable approach than measuring only Fz(t). 相似文献
18.
A crystal and molecular structure determination of MnCl 2(bpy) showed that it exists as polymeric octahedral [MnCl 2(bpy)] n. [MnCl 2(bpy) n crystallizes in the monoclinic space group I2/ a with A = 7.007(1), B = 9.200(1), C = 16.495(1) Å, β = 91.313(5)° and Z = 4. On the basis of 979 unique observed reflections with I 2.5σ( I) the structure was refined to R = 0.032. 相似文献
19.
1. The effect of low oxygen concentration on the oxidation-reduction states of cytochrome c and of pyridine nucleotide, on Ca 2+ uptake, on the energy-linked reduction of pyridine nucleotide by succinate, and on the rate of oxygen consumption have been examined under various metabolic conditions, using pigeon heart mitochondria. 2. The oxygen concentration required to provide half-maximal reduction of cytochrome c (p50c) ranges from 0.27 to 0.03 μM (0.2-0.02 Torr) depending upon the metabolic activity. There is a linear increase of the p50c value with increasing respiratory rate. 3. The fraction of the normoxic respiration that is observed at p50c is 70–90% under State 4 conditions, but is 30% under State 3 conditions. 4. The oxygen requirement for half-maximal reduction of pyridine nucleotide (p50PN) varies less than p50c, being 0.08 μM in State 3 and 0.06 μM in the uncoupled state. 5. The ability of the mitochondria to exhibit an energy-linked reduction of pyridine nucleotide by succinate disappears at an oxygen concentration of 0.09 μM (0.06 Torr). Below this oxygen concentration, endogenous Ca2+ begins to be released from the mitochondria. Thus, the critical oxygen concentration for bioenergetic function of mitochondria corresponds approximately to 50% reduction of pyridine nucleotide (p50PN). 相似文献
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