Maximum Oxidation Rate Research Articles

An Approach to Defining the Upper Safe Limits of Amino Acid Intake

The existing data on the safe upper limits of amino acid intake in humans is essentially observational; how much do individuals ingest and what side effects do they have? There are numerous studies in humans comparing the effects of high doses of amino acids given as protein bound vs. as free amino acids. These studies have shown that protein-bound amino acids have much less effect on plasma levels of the test amino acid, because protein intake stimulates protein synthesis as another sink for the increased amino acid intake. In practice, the highest amino acid intakes occur with free amino acid supplements that may be ingested by athletes who believe that the amino acids will benefit them in training and/or performance. Previously, in a piglet study, we were able to define the point at which maximal phenylalanine oxidation occurred, above which plasma phenylalanine concentration and body balance rose exponentially. We regard this value of maximal disposal (oxidation) of an amino acid as one metabolic marker of the upper limit of intake. Recently, others have demonstrated a similar maximal oxidation rate for leucine in rats. Based on these experimental data and the paucity of published human data in controlled experiments, we think that a systematic approach needs to be undertaken to define the maximal oxidation rate for all dietary indispensable amino acids and other amino acids that may be ingested in excess by humans. We believe that this will provide a rational basis to begin to define the upper limits of tolerance for dietary amino acids. However, some amino acids, such as threonine and methionine, will be more difficult to study, because they have more than 1 route of disposal or very complex metabolic regulation, in which case defining their upper limits will be more multifaceted.

Methodological aspects of crossover and maximum fat-oxidation rate point determination

Aim Indirect calorimetry during exercise provides two metabolic indices of substrate oxidation balance: the crossover point (COP) and maximum fat oxidation rate (LIPOXmax). We aimed to study the effects of the analytical device, protocol type and ventilatory response on variability of these indices, and the relationship with lactate and ventilation thresholds. Methods After maximum exercise testing, 14 relatively fit subjects (aged 32 ± 10 years; nine men, five women) performed three submaximum graded tests: one was based on a theoretical maximum power (tMAP) reference; and two were based on the true maximum aerobic power (MAP). Gas exchange was measured concomitantly using a Douglas bag (D) and an ergospirometer (E). Results All metabolic indices were interpretable only when obtained by the D reference method and MAP protocol. Bland and Altman analysis showed overestimation of both indices with E versus D. Despite no mean differences between COP and LIPOXmax whether tMAP or MAP was used, the individual data clearly showed disagreement between the two protocols. Ventilation explained 10–16% of the metabolic index variations. COP was correlated with ventilation ( r = 0.96, P < 0.01) and the rate of increase in blood lactate ( r = 0.79, P < 0.01), and LIPOXmax correlated with the ventilation threshold ( r = 0.95, P < 0.01). Conclusion This study shows that, in fit healthy subjects, the analytical device, reference used to build the protocol and ventilation responses affect metabolic indices. In this population, and particularly to obtain interpretable metabolic indices, we recommend a protocol based on the true MAP or one adapted to include the transition from fat to carbohydrate. The correlation between metabolic indices and lactate/ventilation thresholds suggests that shorter, classical maximum progressive exercise testing may be an alternative means of estimating these indices in relatively fit subjects. However, this needs to be confirmed in patients who have metabolic defects.

Estimation of mass transport parameters of gases for quantifying CH4 oxidation in landfill soil covers

Methane (CH(4)), which is one of the most abundant anthropogenic greenhouse gases, is produced from landfills. CH(4) is biologically oxidized to carbon dioxide, which has a lower global warming potential than methane, when it passes through a cover soil. In order to quantify the amount of CH(4) oxidized in a landfill cover soil, a soil column test, a diffusion cell test, and a mathematical model analysis were carried out. In the column test, maximum oxidation rates of CH(4) (V(max)) showed higher values in the upper part of the column than those in the lower part caused by the penetration of O(2) from the top. The organic matter content in the upper area was also higher due to the active microbial growth. The dispersion analysis results for O(2) and CH(4) in the column are counter-intuitive. As the upward flow rate of the landfill gas increased, the dispersion coefficient of CH(4) slightly increased, possibly due to the effect of mechanical dispersion. On the other hand, as the upward flow rate of the landfill gas increased, the dispersion coefficient of O(2) decreased. It is possible that the diffusion of gases in porous media is influenced by the counter-directional flow rate. Further analysis of other gases in the column, N(2) and CO(2), may be required to support this hypothesis, but in this paper we propose the possibility that the simulations using the diffusion coefficient of O(2) under the natural condition may overestimate the penetration of O(2) into the soil cover layer and consequently overestimate the oxidation of CH(4).

Organophosphorous plant growth regulator Melaphen: Resistance of plant and animal cells to stress factors

The addition of the organophosphorous plant growth regulator Melaphen (4 × 10−12 M) to the incubation medium increases the maximum rate of oxidation of NAD-dependent substrates in rat liver and sugar beet root mitochondria. In addition, Melaphen stimulates electron transport during oxidation of succinate by rat liver mitochondria, but has no effect on the rate of this substrate oxidation in sugar beet root mitochondria. In storage organs of plants, the rate of oxidation of NAD-dependent substrates by mitochondria is relatively low. By stimulating the activity of NAD-dependent dehydrogenases, Melaphen stimulates energy metabolism in the cells and manifests adaptogenic activity by accelerating the germination of seeds. Melaphen does not influence the fluorescence of lipid peroxidation (LPO) products in mitochondria non-exposed to stress, but decreases 1.5–2 fold the LPO fluorescence in rat liver mitochondria exposed to cold stress and artificially “aged” sugar beet root mitochondria. Besides, Melaphen increases the rate of electron transport in a terminal site of respiratory chains of plant and animal mitochondria and decreases LPO. The data obtained testify to antistress activity of Melaphen.

Sulphuric acid and Pt treatment of the photocatalytically active titanium dioxide

The study focuses on preparation, surface sites characterization and catalytic activity testing of pure (TiO 2), sulfated (TiO 2-S), loaded with 1 wt% Pt (TiO 2-Pt) and platinized/sulfated (TiO 2-Pt-S) high surface area anatase TiO 2 (100% anatase, 340 m 2/g). Sulfation was performed in 4 M H 2SO 4 solution and was not followed by a high temperature calcination. TEM images reveal the formation of a 3 Å amorphous layer over TiO 2 and TiO 2-Pt surface after their sulfation. Infrared spectrum of TiO 2-S contains additional absorption bands at 1235, 1333 and 1378 cm −1 that are assigned to S O stretch and distorted adsorbed SO 4 2 − vibrations. Low temperature CO adsorption and organic species adsorption from heptane solutions was performed for characterization of surface sites. TiO 2-S showed 3–5 cm −1 shift of adsorbed CO absorption band compared to initial TiO 2. The quantity of adsorbed CO increased by a factor of 1.5 for TiO 2-S indicating the increase of the quantity of surface Lewis sites. Sulfation also resulted in disappearance of OH groups having absorption band at 3690 cm −1 that was attributed to substitution by monodentate and bidentate sulfates. Four bases and two acids with different p K were used as probes in solution titration revealing that the quantity of different acid sites in TiO 2-S increases 1.07–2.17 times. Unexpectedly the quantity of acid and base sites in TiO 2-Pt-S decreases relatively to other catalysts studied. Catalytic activity of the samples in acetone deep photooxidation was measured as a function of acetone vapor concentration in a flow-circulating reactor. All dependences are well described by the one site Langmuir–Hinshelwood kinetic model. The maximum oxidation rate was similar for all samples and was observed at acetone concentration above 1500 ppm. However, in the range of low acetone concentration the activity of TiO 2-Pt-S was about triple of pure TiO 2 activity. The high activity of sulfated/platinized and sulfated TiO 2 is due to the much increased acetone adsorption constant.

Effects of an eight-month weight-control program on body composition and lipid oxidation rate during exercise in obese children

To investigate the effects of an 8-month multidisciplinary weight-control program, including 2 h/week of moderate physical activity, nutritional education lessons and psychological follow-up, on body composition and lipid oxidation rate during exercise in obese children. Nineteen (7 boys and 12 girls) obese children, aged 8-12 yr [mean body mass index (BMI) z-score: 2.3 and fat mass: 35.8%] participated in this study. Before and at the end of the weight-control period body composition was assessed by bioelectrical impedance, lipid oxidation rate by indirect calorimetry during a graded exercise test, and time devoted to various activities and energy intake in free-living conditions by questionnaire. All children completed the study, at the end of which BMI decreased significantly by mean 0.6+/-0.5 and 0.5+/-0.8 kg/m2, in boys and girls, respectively (p<0.05), and fat mass (FM) decreased by 1.7+/-2.8 and 1.4+/-1.3 kg in boys and girls, respectively (p<0.05). In addition, lipid oxidation rate during exercise increased significantly throughout the graded exercise test up to 21% at maximal lipid oxidation rate which happened at 48+/-5% of maximal oxygen uptake (VO2max), corresponding to 64+/-5% of maximal heart rate. Time spent at sedentary and very light physical activities decreased (p<0.001) to the benefit of recreational activities at home. Multidisciplinary weight-control program, with moderate-intensity physical activities, induced decreases in FM without decreases in free FM, increases in VO2max, lipid oxidation rate during exercise, and time devoted to recreational activities in free-living conditions.

HDL Atheroprotection by Aerobic Exercise Training in Type 2 Diabetes Mellitus

In this study we analyzed the role played by aerobic exercise training in the plasma lipoprotein profile, prebeta 1-HDL concentration, and in the in vitro HDL3 ability to remove cholesterol from macrophages and inhibit LDL oxidation in type 2 diabetes mellitus (DM) patients and control subjects, in the fasting and postprandial states. Healthy controls (HTC, N = 11; 1 M/10 F) and subjects with type 2 diabetes mellitus (DMT, N = 11; 3M/8F) were engaged in a 4-month aerobic training program, and compared with a group of sedentary subjects with type 2 diabetes mellitus (DMS, N = 10; 4 M/6 F). All groups were submitted to an oral fat load test to analyze all parameters, both at the beginning of the investigation protocol (basal) and at the end of the study period (final). Exercising did not modify body weight, BMI, plasma concentrations of total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides (TG), glucose, insulin, or HOMA-IR, but it reduced the waist circumference. The HDL3 composition did not change, and its ability to remove cell cholesterol was unaltered by aerobic training. In DMT but not in HTC, aerobic training improved 15% the HDL3 protective effect against LDL maximal oxidation rate in the fasting state, and reduced 24% the plasma prebeta 1-HDL concentration in the postprandial state, suggesting an enhanced prebeta 1-HDL conversion into larger, more mature HDL particles. In this regard, regular aerobic exercise enriched HDL2 with TG in the fasting and postprandial states in HTC and in the fasting phase in DMT. Our results show that aerobic exercise training in diabetes mellitus improves the HDL efficiency against LDL oxidation and favors HDL maturation. These findings were independent of changes in insulin resistance and of the rise of plasma HDL cholesterol concentration.

Responses of oxidation rate and microbial communities to methane in simulated landfill cover soil microcosms

CH4 oxidation capacities and microbial community structures developed in response to the presence of CH4 were investigated in two types of landfill cover soil microcosms, waste soil (fine material in stabilized waste) and clay soil. CH4 emission fluxes were lower in the waste soil cover over the course of the experiment. After exposure to CH4 flow for 120 days, the waste soil developed CH4 oxidation capacity from 0.53 to 11.25–13.48μmol CH4gd.w.−1h−1, which was ten times higher than the clay soil. The topsoils of the two soil covers were observed dried and inhibited CH4 oxidation. The maximum CH4 oxidation rate occurred at the depth of 10–20cm in the waste soil cover (the middle layer), whereas it took place mainly at the depth of 20–30cm in the clay soil cover (the bottom layer). The amounts of the phospholipid fatty acid (PLFA) biomarks 16:1ω8c and 18:1ω8c for type I and II methanotrophs, respectively, showed that type I methanotrophic bacteria predominated in the clay soil, while the type II methanotrophic bacteria were abundant in the waste soil, and the highest population in the middle layer. The results also indicated that a greater active methanotrophic community was developed in the waste soil relative to the clay soil.

Prediction of Glucose Oxidation Rate during Exercise

Recently, the relationship between percentage maximal heart rate vs. glucose oxidation rate has been proposed as a tool for estimating glucose oxidation rate during exercise in insulin-dependent diabetic patients. The reliability of this relationship and its applicability to long-term exercise is evaluated. Eight healthy volunteers performed a graded cycloergometric exercise (10-min steps at 30, 50, 70, 90 % of ventilatory threshold). Heart rate and glucose oxidation rate (by indirect calorimetry) were measured during the last 5 min of each step. Volunteers underwent then three 1-hour constant intensity rides at 40, 60, 80 % of ventilatory threshold. Heart rate was recorded continuously; glucose oxidation rate was determined over 15-min periods. The percentage maximal heart rate vs. glucose oxidation rate relationship obtained from the graded exercise matched that previously reported. Independently of intensity, glucose oxidation rates observed during the 1-hr rides were linearly related to the estimated ones (R(2)>0.96, p<0.001), being, however, progressively over-estimated in subsequent exercise periods. The proposed correction yields values close to the identity line (y=1.001 x x; R2=0.974, p<0.001), the difference between observed and "corrected" values amounting to 0.23+/-2.17 mg x min (-1) x kg (-1). In conclusion, glucose oxidation rate can be estimated from heart rate, once proper correction factors are applied for long duration exercises.

A new approach on the thermal stability of SDS copolymer for HMPSA, Part I: Oxidation kinetics for the whole process

The poor aging property of the styrene–diene–styrene (SDS) triblock elastomer copolymer hot-melt pressure-sensitive adhesives (HMPSAs) has raised the importance of research on the aging and anti-aging properties of SDS triblock copolymers, such as styrene–butadiene–styrene (SBS) and styrene–isoprene–styrene (SIS). A mechanistic scheme based on the standard scheme for radical chain oxidation, but taking into account the decomposition of the oxidation-induced peroxide, was built. The kinetic equation of oxygen uptake was deduced from the proposed mechanism, which is composed of a set of reasonable parameters. The relationships among the parameters to induction time, maximum oxygen uptake and the maximum oxidation rate were examined. Numerical simulation methods were established to obtain parameters from the experiment data, by which most kinetic equations of oxygen uptake of the ingredients for HMPSAs were numerically fitted and the relativity of the model to the data was discussed. The study results should prove useful for future studies on the anti-aging performance of other materials.

亜硝酸酸化細菌群の窒素酸化履歴に対する最大亜硝酸酸化速度の応答

A factor that controls maximum cell-specific nitrite oxidation rate was examined using the enrichment culture of Nitrobacter. Increasing or decreasing nitrite loading changed the content of Q-10, which served as a hydrogen carrier in the electron transport chain of Nitrobacter, which varied the maximum cell-specific nitrite oxidation rate. That is, the amount of oxidized nitrite, which is the sole electron donor, changed in the maximum cell-specific nitrite oxidation rate. Then, a dynamic change in maximum cell-specific nitrite oxidation rate was examined at short time intervals with increasing nitrite loading. Consequently, it was found that the maximum cell-specific nitrite oxidation rate began to increase after reaching a certain amount of oxidized nitrite. It was additionally indicated that the maximum cell-specific nitrite oxidation rate presumably had an upper limit and increased gradually near the limit. From the results, the response time and variation in maximum cell-specific nitrite oxidation rate are likely to be determined on the basis of the hysteresis of nitrite oxidation by nitrite-oxidizing bacteria.

The influence of relative humidity on iron corrosion under proton irradiation

With regard to the storage for high-level radioactive waste and the reversible period of a geological repository, the influence of proton irradiation on the indoor atmospheric corrosion of iron has been investigated in relation to the relative humidity (RH) in the atmosphere. Irradiation experiments were performed using a 3-MeV extracted proton beam. Relative humidity varies from 0% to 85%. Before and after each irradiation, the surfaces of the sample were characterised by Rutherford backscattering spectrometry in order to determine oxygen concentrations in the metal. The maximum oxidation rate was observed for 45% RH in air under proton irradiation and was compared with literature data without irradiation where the maximum oxidation rate was observed at 95% RH. The experimental results are discussed on the basis of the Langmuir–Hinshelwood (LH) model: they are explained by the contrast between the adsorption of O 2 and H 2O species on the active cathodic sites of the iron surface and by the formation of H +(H 2O) n .

Comparison of ferric iron generation by different species of acidophilic bacteria immobilized in packed-bed reactors

Flooded packed-bed bioreactors, prepared by immobilizing four different species of acidophilic iron-oxidizing bacteria on porous glass beads, were compared for their ferric iron-generating capacities when operated in batch and continuous flow modes over a period of up to 9 months, using a ferrous iron-rich synthetic liquor and acid mine drainage (AMD) water. The bacteria used were strains of Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, a Ferrimicrobium-like isolate (TSTR) and a novel Betaproteobacterium (isolate PSTR), which were all isolated from relatively low-temperature mine waters. Three of the bacteria used were chemoautotrophs, while the Ferrimicrobium isolate was an obligate heterotroph. Greater biomass yields achievable with the Ferrimicrobium isolate resulted in greater iron oxidation efficiency in the newly commissioned bioreactor containing this bacterium, though long-term batch testing with organic carbon-free solution resulted in similar maximum iron oxidation rates in all four bioreactors. Two of the bioreactors (those containing immobilized L. ferrooxidans and Ferrimicrobium TSTR) were able to generate significantly lower concentrations of ferrous iron than the others when operated in batch mode. In contrast, when operated as continuous flow systems, the bioreactor containing immobilized PSTR was superior to the other three when challenged with either synthetic or actual AMD at high flow rates. The least effective bacterium overall was At. ferrooxidans, which has previously been the only iron-oxidizer used in the majority of reports describing ferric iron-generating bioreactors. The results of these experiments showed that different species of iron-oxidizing acidophiles have varying capacities to oxidize ferrous iron when immobilized in packed-bed bioreactors, and that novel isolates may be superior to well-known species.

Oxygen availability and PCr recovery rate in untrained human calf muscle: evidence of metabolic limitation in normoxia

In contrast to their exercise-trained counterparts, the maximal oxidative rate of skeletal muscle in sedentary humans appears not to benefit from supplemental O(2) availability but is impacted by severe hypoxia, suggesting a metabolic limitation either at or below ambient O(2) levels. However, the critical level of O(2) availability at which maximal metabolic rate is reduced in sedentary humans is unknown. Using (31)P magnetic resonance spectroscopy and arterial oximetry, phosphocreatine (PCr) recovery kinetics and arterial oxygenation were assessed in six sedentary subjects performing 5-min bouts of plantar flexion exercise followed by 6 min of recovery. Each trial was repeated while breathing one of four different fractions of inspired O(2) (FI(O(2))) (0.10, 0.12, 0.15, and 0.21). The PCr recovery rate constant (a marker of oxidative capacity) was unaffected by reductions in FI(O(2)), remaining at a value of 1.5 +/- 0.2 min(-1) until arterial O(2) saturation (Sa(O(2))) fell to less than approximately 92%, the average value reached breathing an FI(O(2)) of 0.15. Below this Sa(O(2)), the PCr rate constant fell significantly by 13 and 31% to 1.3 +/- 0.2 and 1.0 +/- 0.2 min(-1) (P < 0.05) as Sa(O(2)) was reduced to 82 +/- 3 and 77 +/- 2%, respectively. In conclusion, this study has revealed that O(2) availability does not impact maximal oxidative rate in sedentary humans until the O(2) level falls well below that of ambient air, indicating a metabolic limitation in normoxia.

Respirometric techniques for assessment of biological kinetics in constructed wetland

The aim of this research was the development of a procedure to measure biological kinetics of organic matter oxidation and nitrification in constructed wetland, by using respirometric techniques. Columns simulating cores of vertical subsurface flow systems were investigated. The oxygen uptake rate (OUR) of the columns was calculated on the basis of the difference of DO concentrations measured continuously at the top and at the bottom of the column. From the respirogram, the following kinetic parameters have been evaluated: maximum rate of oxidation of readily biodegradable COD, maximum rate of nitrification, endogenous respiration of the biomass grown inside the bed. In order to improve the interpretation of the respirograms, additional respirometric tests were carried out on the wetland columns by using pure substrates, such as acetate (carbon source) and ammonium (substrate for nitrification). The kinetic parameters obtained from respirograms can be useful for control and design of constructed wetlands or for improving nutrient and carbon mass balances.

English

Flow-through reactor field experiments were conducted at two large net alkaline mine discharges in central Pennsylvania. The goal was to drive off CO2, increase pH, and document increased Fe(II) oxidation rates compared to passive treatment methods. Both discharges were low Mn, low Al, net alkaline discharges with pH of ≈ 5.7 and Fe(II) concentration of ≈ 16 mg/L. Flow rates were ≈ 3000 and 15000 L/min. Three-hour aeration experiments with flow rates scaled to a 14-L reactor resulted in pH increases from 5.7 to greater than 7, temperature increases from 12 to 22 oC, dissolved oxygen increases to saturation with respect to the atmosphere, and Fe(II) concentration decreases to less than 0.05 mg/L. The same experiment at one of the sites with a 13-hour run time and no active aeration had a pH change from 6.1 to 6.3 and decrease in Fe(II) concentration from 16.3 to 13.8 mg L -1 . Results from an Fe(II) oxidation model, using field-measured pH, temperature, dissolved oxygen, and initial Fe(II) concentration and written in a differential equation solver, were the same as the field experiments within analytical uncertainty. The maximum oxidation rate was 1.3 x 10 -4 mol L -1 sec -1 . The model was also modified to predict alkalinity, PCO2, and pH changes based on initial conditions and aeration rate. This modified model also matched the data within analytical uncertainty, is more predictive than the first model, and should serve as a tool for predicting pond size needed for aerated Fe(II) oxidation at the field scale without the need for field pilot studies. Using a published Fe removal rate of 20 g m -2 day -1 and Fe loading from field data, 3.6 x 10 3 and a 3.0 x 10 4 m 2 passive oxidation treatment ponds would be required for Site 21 and Packer 5 discharges, respectively. Fe(II) oxidation modeling of actively aerated systems predicted that a 1 m deep pond with 10 times less area would be adequate to lower Fe(II) concentrations to less than 1 mg L -1 at summer and winter temperatures for both sites. The use of active aeration for net alkaline discharges with high CO2 concentrations can result in considerably reduced treatment area for oxidation and may lower treatment costs, but settling of iron hydroxides was not considered in this study. The reduced capital cost for earthmoving will need to be compared to energy and maintenance costs for aeration.

Selective oxidation of soot over Cu doped ceria/ceria–zirconia catalysts

Copper doped ceria and ceria–zirconia mixed oxides were prepared using the citric acid sol–gel method. The temperature-programmed oxidation (TPO) results showed that the Cu modification helped to improve the activity and selectivity of ceria and ceria–zirconia for soot catalytic oxidation. The CO-TPR results showed that Cu–Ce had a better reducibility than pure ceria at low temperatures. After ageing at 800 °C for 20 h in flow air, CuO–CeO2 showed the maximum soot oxidation rate at 378 and 519 °C under tight and loose contact conditions, respectively, achieving a nearly 100% selectivity to CO2 production. This effect may be attributed to the existence of well dispersed copper oxide species strongly interacting with the ceria surface, which may decrease the activation energy of soot oxidation. A conceivable mechanism of this synergetic effect was proposed.

Optimizing fat oxidation through exercise in severely obese Caucasian adolescents

To measure the contribution of substrate oxidation to energy expenditure during cycling at different workloads and to identify the exercise intensity that elicits the maximum fat oxidation rate in groups of severely obese or nonobese Caucasian adolescents. A total of 30 severely obese subjects (mean body mass index, BMI = 34.7 kg/m2; fat-mass = 39.9%) and 30 nonobese sedentary adolescents (mean BMI = 22.7 kg/m2; fat-mass = 21.8%) aged 14-16 years, participated in this study. Body composition was assessed by bioelectrical impedance. Peak oxygen uptake (VO2peak) and maximal fat oxidation rate were determined with indirect calorimetry by using a graded exercise test on an electromagnetically braked cycle ergometer. Predicted VO2max were expressed in absolute (l/min) and relative (ml/kg FFM/min) values, and maximal work rates were not significantly different between obese and nonobese adolescents, but were significantly higher in boys than in girls. No significant differences in fat oxidation rates were found in obese and nonobese sedentary adolescents during the graded exercise test. Maximal fat oxidation was observed at an exercise intensity corresponding to (mean +/- SD) 41 +/- 3%VO2max or 58 +/- 3% HRmax. At this exercise intensity, fat oxidation rates were higher in boys than in girls (0.32 +/- 0.02 g/min vs. 0.25 +/- 0.02 g/min, P < 0.001). Severely obese and sedentary nonobese adolescents reached maximal fat oxidation rates at 41%VO2max, which corresponds to 58% HRmax. At this exercise intensity, fat oxidation rates were higher in boys than in girls probably due to higher VO2max and absolute workload during the exercise steps for boys compared with those for girls.

Kinetic Constant Variability in Bacterial Oxidation of Elemental Sulfur

Wide ranges of growth yields on sulfur (from 2.4 x 10(10) to 8.1 x 10(11) cells g(-1)) and maximum sulfur oxidation rates (from 0.068 to 1.30 mmol liter(-1) h(-1)) of an Acidithiobacillus ferrooxidans strain (CCM 4253) were observed in 73 batch cultures. No significant correlation between the constants was observed. Changes of the Michaelis constant for sulfur (from 0.46 to 15.5 mM) in resting cells were also noted.

No effect of menstrual cycle on LDL oxidizability and particle size

Objectives Premenopausal women have a lower incidence of cardiovascular disease than men, but this female advantage disappears after menopause, suggesting that female sex hormones exert some cardioprotective effects. One of the mechanisms proposed to explain this cardioprotection is the antioxidant properties of estrogens. The aim of this work was to assess whether fluctuations in ovarian hormones, particularly 17β-estradiol (E 2), during the menstrual cycle were associated with changes in the low-density lipoprotein (LDL) particle size, fatty acyl composition, α-tocopherol content and in vitro oxidizability. Methods Twenty-eight healthy premenopausal women (mean age: 32.2 years) participated in the study. Blood was drawn on days 3 (menstrual phase), 14 (follicular phase) and 22 (luteal phase) of the menstrual cycle for plasma determinations and LDL isolation. Plasma E 2, progesterone, follicle-stimulating hormone and luteinizing hormone were determined by immunoassay. LDL oxidation by Cu 2+- and 2,2′-azobis (2-amidinopropane) was measured by the formation of conjugated dienes, LDL particle size by quasi-elastic light scattering, fatty acyl composition by gas chromatography, α-tocopherol by reversed phase HPLC. A within-subjects analysis of variance was performed to determine significant differences of the variables over the course of a subject's menstrual cycle. Results The LDL oxidizability indices (lag time before the onset of propagation and the maximal oxidation rate) did not change during the menstrual cycle. The LDL particle size (24.8 ± 1.7 nm diameter), α-tocopherol (11.7 ± 3.7 nmol/mg LDL protein) and fatty acyl composition also remained constant. Conclusions The LDL physicochemical properties and oxidizability are not affected by menstrual cycle phase.