共查询到20条相似文献,搜索用时 15 毫秒
1.
J.F. Steffensen K. Johansen C.D. Sindberg J.H. Sørensen J.L. Møller 《Journal of experimental marine biology and ecology》1984,84(2):173-178
Ventilation was measured directly in the hagfish, Myxine glutinosa L., by means of an electro-magnetic blood flowmeter. Ventilatory flow and frequency increased from 0.86 ± 0.27 ml·min?, and 18.2 ± 5.1·min?, respectively, at 7°C to 1.70 ± 0.20 ml·min?, and 70.1 ± 9.5·min? at 15 ·C.Standard oxygen consumption,V?O2, was measured in non-buried hagfish. V?O2 was 0.57 ± 0.17μl O2·g?1·min?1 at 7°C, and 0.85 ± 0.12μl O2·g?1·min?1 at 15°C. 相似文献
2.
The paper describes a sensitive, rapid, and precise photometric method for the continuous and discontinuous determination of O2, CO2, and CO. The method is based on highly specific color reactions: O2 is determined by its reaction with alkaline catechol + Fe2+ yielding intensively colored products, CO2 is determined by its color reaction with a solution of fuchsin + hydrazine; and CO is determined by its reaction with hemoglobin. The basic experimental equipment is that of the AutoAnalyzer (cf.Wolf, Zander, and Lang, 1976, Anal. Biochem.74, 585), with an additional chamber for the injection of small gas samples in the case of the discontinuous analysis. Continuously analyzing in a standardized gas flow of 1 ml · min?1 (STPD), the lower limits of the sensitivities are 50 ppm for O2, 100 ppm for CO2, and 50 ppm for CO. The discontinuous analysis of the three gases requires the basic experimental equipment plus an airtight chamber. The lower limits of the amounts are 0.1 μl (STPD) for O2, 0.2 μl for CO2, and 0.1 μl for CO. 相似文献
3.
Tapan K. Ghosh Amita Moitra Gopal K. Kunwar Jyoti S. D. Munshi 《Ichthyological Research》1986,33(3):280-285
Measurements of bimodal oxygen uptake have been made in a freshwater air-breathing fish,Notopterus chitala at 29.0±1(S.D.)°C. xhe mean oxygen uptake from continuously flowing water without any access to air, was found to be 3.58±0.37 (S.E.) ml O2 · h?1 and 56.84+4.29 (S.E.) ml O2 · kg?1 · h?1 for a fish weighing 66.92 + 11.27 (S.E.) g body weight. In still water with access to air, the mean oxygen uptake through the gills were recorded to be 2.49 ± 0.31 (S.E.) ml O2 · h?1 and 38.78 ± 1.92 (S.E.) ml O2 · kg?1 · h?1 and through the accessory respiratory organs (swim-bladder) 6.04±0.87 (S.E.) ml O2 · h?1 and 92.32±2.91 (S.E.) ml O2 · kg?1 · h?1 for a fish averaging 66.92±11.27 (S.E.) g. Out of the total oxygen uptake (131.10 ml O2 · kg?1 · h?1), about 70% was obtained through the aerial route and the remainder 30% through the gills. 相似文献
4.
W.J. van Aardt 《African Journal of Aquatic Science》2013,38(1-2):16-36
Summary The oxygen consumption rate (?O2) for Potamonauteus warreni Calman (= Potamon warreni (Calman) kept in 25 °C water was 34,4 μmol 1?1 O2 kg?1 and after 72 hours in 98% R.H. air the rate was 31,9 μmol 1?1 O2 kg?1 min?1. The ?O2 values for each of the two groups are not significantly different (P > 0,05). The partial oxygen tension of pre-branchial (v = venous) haemolymph (PvCO2) is 15,3 mm Hg in water and 13,0 mm Hg in air); partial carbon dioxide tension of pre-branchial (v) haemolymph (PvCO2) is 13,2 mm Hg in water and 13,0 mm Hg in air); the total carbon dioxide concentration in pre-branchial (v) haemolymph (CvCO2) tot. is 12,3 mmol 1?1 in air and 13,9 mmol 1?1 in water) are not significantly different for the two groups (P > 0,05). The haemolymph pH and the lactate concentration for crabs in water was found to be 7,51 and 0,38 mmol 1?1 respectively. No significant differences were found in pre-branchial haemolymph oxygen tension, carbon dioxide tension, total carbon dioxide content, haemolymph pH, lactate level, chloride concentration, P50 and haemocyanin-oxygen cooperativity in control crabs kept in water, and experimental crabs held in air for 72 hours. The chloride concentration, (327,0 mmol 1?1) for crabs kept in water does not differ from that of crabs held in air for 72 hours but is at least 15% higher than the sodium concentration (255 mmol 1?1) for crabs kept in water. The gill surface area is 520 mm2 g?1 wet body mass; on average 9,2 gill platelets (lamellae) can be found on a gill length of one millimetre. Each lamella is spaced 60–70 μm apart, each with a thickness of 30–40 μm. It is concluded that P. warreni may be described as a truly amphibious fresh-water crab. 相似文献
5.
Xylem sap flow as a major pathway for oxygen supply to the sapwood of birch (Betula pubescens Ehr.) 总被引:2,自引:1,他引:1
D. GANSERT 《Plant, cell & environment》2003,26(11):1803-1814
The role of xylem sap flow as an aqueous pathway for oxygen supply to the wood parenchyma of Betula pubescens saplings was investigated. Using micro‐optode sensors the oxygen status of the sapwood was quantified in relation to mass flow of xylem sap. Sap flow was gradually reduced by an increasing oxygen depletion in the root space. The effect of sap flow on radial O2 transport between stem and atmosphere was assessed by a stoichiometrical approach between respiratory CO2 production and O2 consumption. Restriction of sap flow set in 36.5 h after the onset of O2 depletion, and was complete after 71 h. Interruption of sap flow drastically increased the O2 deficit in the sapwood to 70%. Sap flow contributed about 60% to the total oxygen supply to the sapwood. Diurnal O2 flow rates varied between 3 and 6.3 nmol O2 m?2 leaf area (LA) s?1 during night‐ and daytime, respectively. Maximum O2 flow rates of 20 nmol O2 m?2 LA s?1 were reached at highest sap flow rates of 5.7 mmol H2O m?2 LA s?1. Sap flow not only affected the oxygen status of the sapwood but also had an effect on radial O2 transport between stem and atmosphere. 相似文献
6.
Hee Jae Kim Aishuak Konarov Jae Hyeon Jo Ji Ung Choi Kyuwook Ihm Han‐Koo Lee Jongsoon Kim Seung‐Taek Myung 《Liver Transplantation》2019,9(32)
A high‐rate of oxygen redox assisted by cobalt in layered sodium‐based compounds is achieved. The rationally designed Na0.6[Mg0.2Mn0.6Co0.2]O2 exhibits outstanding electrode performance, delivering a discharge capacity of 214 mAh g?1 (26 mA g?1) with capacity retention of 87% after 100 cycles. High rate performance is also achieved at 7C (1.82 A g?1) with a capacity of 107 mAh g?1. Surprisingly, the Na0.6[Mg0.2Mn0.6Co0.2]O2 compound is able to deliver capacity for 1000 cycles at 5C (at 1.3 A g?1), retaining 72% of its initial capacity of 108 mAh g?1. X‐ray absorption spectroscopy analysis of the O K‐edge indicates the oxygen‐redox species (O2?/1?) is active during cycling. First‐principles calculations show that the addition of Co reduces the bandgap energy from ≈2.65 to ≈0.61 eV and that overlapping of the Co 3d and O 2p orbitals facilitates facile electron transfer, enabling the long‐term reversibility of the oxygen redox, even at high rates. To the best of the authors' knowledge, this is the first report on high‐rate oxygen redox in sodium‐based cathode materials, and it is believed that the findings will open a new pathway for the use of oxygen‐redox‐based materials for sodium‐ion batteries. 相似文献
7.
Abstract: A previous study of the metabolism of 6-[18F]-fluoro-l -3,4-dihydroxyphenylalanine (FDOPA) in rats pretreated with carbidopa contained information amenable to kinetic analysis. Using these data, tracer transfer coefficients and metabolic rate constants were estimated. After intravenous injection, FDOPA in circulation was O-methylated (kD0 = 0.055 min?1), and the metabolite (O-methyl-FDOPA) escaped from plasma with a rate constant (kM?1) of 0.01 min?1. The initial clearance of FDOPA to striatum (KD1) was 0.07 ml g?1 min?1, and the equilibrium distribution volume (VDe) was 0.67 ml g?1. The initial clearance of O-methyl-FDOPA to striatum (KM1) was 0.08 ml g?1 min?1, and the equilibrium distribution volume (VMe) was 0.75 ml g?1. The rate constant of FDOPA decarboxylation (kD3) was 0.17 min?1 in striatum. The elimination of 6-[18F]fluorodopamine (FDA) from striatum suggested an apparent rate constant for monoamine oxidase activity (k′7) of 0.055 min?1. 6-[18F]Fluorohomovanillic acid (FHVA) was formed from 6-[18F]fluoro-l -3,4-dihydroxyphenylacetic acid with a rate constant (k11) of 0.083 min?1, and FHVA was eliminated from striatum (k9) with a rate constant of 0.12 min?1. The steady-state concentration ratios of FDA and its metabolites were shown to be functions of these rate constants. 相似文献
8.
Stewart Farling Tobias L. Straube Travis P. Vesel Nick Bottenus Bruce Klitzman Ira M. Cheifetz Marc A. Deshusses 《Biotechnology and bioengineering》2021,118(1):345-356
Despite hypoxic respiratory failure representing a large portion of total hospitalizations and healthcare spending worldwide, therapeutic options beyond mechanical ventilation are limited. We demonstrate the technical feasibility of providing oxygen to a bulk medium, such as blood, via diffusion across nonporous hollow fiber membranes (HFMs) using hyperbaric oxygen. The oxygen transfer across Teflon® membranes was characterized at oxygen pressures up to 2 bars in both a stirred tank vessel (CSTR) and a tubular device mimicking intravenous application. Fluxes over 550 ml min?1 m?2 were observed in well‐mixed systems, and just over 350 ml min?1 m?2 in flow through tubular systems. Oxygen flux was proportional to the oxygen partial pressure inside the HFM over the tested range and increased with mixing of the bulk liquid. Some bubbles were observed at the higher pressures (1.9 bar) and when bulk liquid dissolved oxygen concentrations were high. High‐frequency ultrasound was applied to detect and count individual bubbles, but no increase from background levels was detected during lower pressure operation. A conceptual model of the oxygen transport was developed and validated. Model parametric sensitivity studies demonstrated that diffusion through the thin fiber walls was a significant resistance to mass transfer, and that promoting convection around the fibers should enable physiologically relevant oxygen supply. This study indicates that a device is within reach that is capable of delivering greater than 10% of a patient's basal oxygen needs in a configuration that readily fits intravascularly. 相似文献
9.
In this study, a new analytical method for erdosteine (ERD) in plasma based on high‐performance liquid chromatography and a fluorimetric detector, is presented. Precolumn derivatization of ERD with 4‐bromomethyl‐7‐methoxy coumarin (BrMmC) and dibenzo‐18‐crown‐6‐ether as a reaction catalyst led to the production of a fluorescent compound. ERD was monitored by fluorescence with an excitation wavelength λext. = 325 nm and emission wavelength λem. = 390 nm. Optimum reaction conditions were carefully studied and optimized. A chromatographic procedure was performed using a C18 column of 150 × 4.6 mm and 3 μm particle size and a mobile phase consisting of methanol:acetonitrile:water (30:30:40, v/v/v) under a flow rate of 0.5 ml min?1. A calibration plot was established covering analyte concentration range 0.2–3.0 μg ml?1; the detection limit was 0.015 μg ml?1 and quantification limit was 0.05 μg ml?1. Mean recovery was 87.33% and relative standard deviation was calculated to be less than 4.4%. The developed method was successfully used to determine pharmacokinetic preparations of ERD subsequent to administration of a 900 mg dose capsule to a healthy 40‐year‐old woman volunteer. 相似文献
10.
Direct evidence for the presence of a rotenone-resistant NADH dehydrogenase on the inner surface of the inner membrane of plant mitochondria 总被引:2,自引:0,他引:2
Submitochondrial particles (SMP) were produced from Jerusalem artichoke (Helianthus tuberosus L.) mitochondria by sonication and differential centrifugation. The SMP were about 50% inside-out as measured by the access of reduced cytochrome c to cytochrome c oxidase. Uncoupled NADH oxidation (1 mM NADH) by the SMP was 120 nmol O2 min?1mg?1, which was reduced to 98 nmol O2 min?1 (mg mitochondrial protein)?1 in the presence of EGTA. In contrast, the oxidation of NADH by intact mitochondria was completely inhibited by EGTA (from 182 to 14 nmol O2 min?1mg?1). The EGTA-resistant NADH oxidation by the SMP is ascribed to the NADH dehydrogenase(s) on the inside of the inner membrane and exposed to the medium in the inside-out SMP. In the presence of EGTA it could be shown that two NADH dehydrogenase activities were present in the SMP. One had an apparent Km of 7 μM for NADH, a Vmax of 80 nmol NADH min?1mg?1, and was rotenone-sensitive. This dehydrogenase is equivalent to the mammalian Complex I NADH dehydrogenase. The other dehydrogenase, which was rotenone-resistant, had a Km of 80 μM and a Vmax of 131 nmol NADH min?1mg?1; it is probably responsible for the rotenone-resistant oxidation of organic acids often observed in plant mitochondria. The redox poise of the pyridine nucleotides had only a small effect on the relative rates of the two internal dehydrogenases. Electron flow through these dehydrogenases appears, therefore, to be regulated mainly by the concentration of NADH in the matrix of the mitochondria. 相似文献
11.
Yuki Watanabe Gregory N. Nishihara Shigemitsu Tokunaga Ryuta Terada 《Phycological Research》2014,62(3):187-196
The effect of irradiance and temperature on the photosynthesis of the red alga, Pyropia tenera, was determined for maricultured gametophytes and sporophytes collected from a region that is known as one of the southern limits of its distribution in Japan. Macroscopic gametophytes were examined using both pulse‐amplitude modulated fluorometry and/or dissolved oxygen sensors. A model of the net photosynthesis–irradiance (P‐E) relationship of the gametophytes at 12°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 46 μmol photons m?2 s?1, and the compensation irradiance was 9 μmol photons m?2 s?1. Gross photosynthesis and dark respiration for the gametophytes were also determined over a range of temperatures (8–34°C), revealing that the gross photosynthetic rates of 46.3 μmol O2 mgchl‐a?1 min?1 was highest at 9.3 (95% Bayesian credible interval (BCI): 2.3–14.5)°C, and the dark respiration rate increased at a rate of 0.93 μmol O2 mgchl‐a?1 min?1°C?1. The measured dark respiration rates ranged from ?0.06 μmol O2 mgchl‐a?1 min?1 at 6°C to ?25.2 μmol O2 mgchl‐a?1 min?1 at 34°C. The highest value of the maximum quantum yield (Fv/Fm) for the gametophytes occurred at 22.4 (BCI: 21.5–23.3) °C and was 0.48 (BCI: 0.475–0.486), although those of the sporophyte occurred at 12.9 (BCI: 7.4–15.1) °C and was 0.52 (BCI: 0.506–0.544). This species may be considered well‐adapted to the current range of seawater temperatures in this region. However, since the gametophytes have such a low temperature requirement, they are most likely close to their tolerable temperatures in the natural environment. 相似文献
12.
An Open‐Structured Matrix as Oxygen Cathode with High Catalytic Activity and Large Li2O2 Accommodations for Lithium–Oxygen Batteries
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Xiaodong Lin Ruming Yuan Senrong Cai Youhong Jiang Jie Lei San‐Gui Liu Qi‐Hui Wu Hong‐Gang Liao Mingsen Zheng Quanfeng Dong 《Liver Transplantation》2018,8(18)
The nonaqueous lithium–oxygen (Li–O2) battery is considered as one of the most promising candidates for next‐generation energy storage systems because of its very high theoretical energy density. However, its development is severely hindered by large overpotential and limited capacity, far less than theory, caused by sluggish oxygen redox kinetics, pore clogging by solid Li2O2 deposition, inferior Li2O2/cathode contact interface, and difficult oxygen transport. Herein, an open‐structured Co9S8 matrix with sisal morphology is reported for the first time as an oxygen cathode for Li–O2 batteries, in which the catalyzing for oxygen redox, good Li2O2/cathode contact interface, favorable oxygen evolution, and a promising Li2O2 storage matrix are successfully achieved simultaneously, leading to a significant improvement in the electrochemical performance of Li–O2 batteries. The intrinsic oxygen‐affinity revealed by density functional theory calculations and superior bifunctional catalytic properties of Co9S8 electrode are found to play an important role in the remarkable enhancement in specific capacity and round‐trip efficiency for Li–O2 batteries. As expected, the Co9S8 electrode can deliver a high discharge capacity of ≈6875 mA h g?1 at 50 mA g?1 and exhibit a low overpotential of 0.57 V under a cutoff capacity of 1000 mA h g?1, outperforming most of the current metal‐oxide‐based cathodes. 相似文献
13.
Twenty-four-hour variations in activity,core temperature,metabolic rate,and respiratory quotient in captive chinese pangolins 总被引:1,自引:0,他引:1
Martha E. Heath 《Zoo biology》1987,6(1):1-10
The circadian rhythms in activity, core temperature (Tc), O2 consumption, CO2 production, and respiratory quotient (RQ) were monitored in four captive Chinese pangolins (Manis pentadactyla). The pangolins were strictly nocturnal, never emerging from their nest before 1600 h, and their intermittent activity continued no later than 0230. As is usual in nocturnal mammals, the highest values observed in Tc, O2 consumption, and CO2 production occurred during the night; the lowest values occurred during the day. The magnitude of the variation in Tc, O2 consumption, CO2 production, and RQ averaged 1.2°C, 1.3 ml O2 kg?1 min?1, 1.2 ml CO2 kg?1 min?1, and 0.24, respectively. The circadian pattern in RQ was independent of activity, Tc, and the metabolic parameters and was of a different character than the patterns exhibited in the other variables. RQ remained constant at either a high or low level for long periods (8–10 h) and then increased or decreased relatively rapidly (1–2h) to the other level as in a square wave, whereas the rhythms in the other variables are similar to sine waves. The sharp increase in RQ was followed by a slow decline in Tc, and the sharp decline in RQ was followed by a slow increase in Tc. 相似文献
14.
The oxidation reaction of H2O2 with KIO4 can produce chemiluminescence (CL) in the presence of the surfactant Tween40 and the CL intensity of the CL system KIO4–H2O2–Tween40 can be strikingly enhanced after injection of tannic acid. On this basis, a flow injection method with CL detection was established for the determination of tannic acid. The method is simple, rapid and effective to determine tannic acid in the range of 7.0 × 10?9 to 1.0 × 10?5 mol/L with a determination limit of 2.3 × 10?9 mol/L. The relative standard deviation is 2.6% for the determination of 5.0 × 10?6 mol/L tannic acid (n = 11). The method has been applied to determine the content of tannic acid in industrial wastewater with satisfactory results. It is believed that the CL reaction formed singlet oxygen 1O2* and the emission was from an excited oxygen molecular pair O2(1Δg)O2(1∑?g) in the KIO4–H2O2–Tween40 reaction. Tween40 played an important role in enhancing stabilization of the excited oxygen molecular pair O2(1Δg)O2(1∑?g) and in increasing CL intensity. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
15.
Carling D. Gerlinsky David A. S. Rosen Andrew W. Trites 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2013,183(5):699-708
The diving capacity of marine mammals is typically defined by the aerobic dive limit (ADL) which, in lieu of direct measurements, can be calculated (cADL) from total body oxygen stores (TBO) and diving metabolic rate (DMR). To estimate cADL, we measured blood oxygen stores, and combined this with diving oxygen consumption rates (VO2) recorded from 4 trained Steller sea lions diving in the open ocean to depths of 10 or 40 m. We also examined the effect of diving exercise on O2 stores by comparing blood O2 stores of our diving animals to non-diving individuals at an aquarium. Mass-specific blood volume of the non-diving individuals was higher in the winter than in summer, but there was no overall difference in blood O2 stores between the diving and non-diving groups. Estimated TBO (35.9 ml O2 kg?1) was slightly lower than previously reported for Steller sea lions and other Otariids. Calculated ADL was 3.0 min (based on an average DMR of 2.24 L O2 min?1) and was significantly shorter than the average 4.4 min dives our study animals performed when making single long dives—but was similar to the times recorded during diving bouts (a series of 4 dives followed by a recovery period on the surface), as well as the dive times of wild animals. Our study is the first to estimate cADL based on direct measures of VO2 and blood oxygen stores for an Otariid and indicates they have a much shorter ADL than previously thought. 相似文献
16.
Ronald J. Lukasiewicz Edward L. Bennett 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,544(2):294-308
High-affinity, specific binding of radiolabeled α-bungarotoxin to particulate fractions derived from rat brain shows saturability (Bmax ≈ 37fmol/mg, KDapp = 1.7 nM) and insensitivity to ionic strength, and is essentially irreversible (Kon = 5 · 106 min?1 · mol?1; Kdisplacement = 1.9 · 10?4 min?1, τ1/2 = 62 h). Subcellular distribution of specific sites is consistent with their location on synaptic junctional complex and post-synaptic membranes. These membrane-bound binding sites exhibit unique sensitivity to cholinergic ligands; pretreatment of membranes with cholinergic agonists (but not antagonists) induces transformation of α-bungarotoxin binding sites to a high affinity form toward agonist. The effect is most marked for the natural agonist, acetylcholine. These results strongly support the notion that the entity under study is an authentic nicotinic acetylcholine receptor. 相似文献
17.
Escherichia coli B were more susceptible to radiation lethality and showed a greater oxygen enhancement ratio when exposed in dilute suspension (1 × 105 cells/ml) than when exposed in dense suspensions (1 × 109 cells/ml). The oxygen enhancement, seen with dilute suspensions, was diminished by superoxide dismutase, catalase, mannitol, or histidine. Heat-denatured superoxide dismutase was without effect. The results are interpreted as indicating a role for O2? plus H2O2 in the oxygen enhancement of radiation lethality, and a scheme is proposed which is consistent with the observations. 相似文献
18.
Hierarchically Porous,Ultrathick, “Breathable” Wood‐Derived Cathode for Lithium‐Oxygen Batteries
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Huiyu Song Shaomao Xu Yiju Li Jiaqi Dai Amy Gong Mingwei Zhu Chunliang Zhu Chaoji Chen Yanan Chen Yonggang Yao Boyang Liu Jianwei Song Glenn Pastel Liangbing Hu 《Liver Transplantation》2018,8(4)
In this work, a hierarchically porous and ultrathick “breathable” wood‐based cathode for high‐performance Li‐O2 batteries is developed. The 3D carbon matrix obtained from the carbonized and activated wood (denoted as CA‐wood) serves as a superconductive current collector and an ideal porous host for accommodating catalysts. The ruthenium (Ru) nanoparticles are uniformly anchored on the porous wall of the aligned microchannels (denoted as CA‐wood/Ru). The aligned open microchannels inside the carbon matrix contribute to unimpeded oxygen gas diffusion. Moreover, the hierarchical pores on the microchannel walls can be facilely impregnated by electrolyte, forming a continuous supply of electrolyte. As a result, numerous ideal triphase active sites are formed where electrolyte, oxygen, and catalyst accumulate on the porous walls of microchannels. Benefiting from the numerous well‐balanced triple‐phase active sites, the assembled Li‐O2 battery with the CA‐wood/Ru cathode (thickness: ≈700 µm) shows a high specific area capacity of 8.58 mA h cm?2 at 0.1 mA cm?2. Moreover, the areal capacity can be further increased to 56.0 mA h cm?2 by using an ultrathick CA‐wood/Ru cathode with a thickness of ≈3.4 mm. The facile ultrathick wood‐based cathodes can be applied to other cathodes to achieve a super high areal capacity without sacrificing the electrochemical performance. 相似文献
19.
Effects of aeration and of corn steep concentration on L-asparaginase production in Escherichia coli
J. Netrval 《Applied microbiology and biotechnology》1980,9(3):185-187
Summary The production of L-asparaginase was investigated in Escherichia coli, growing under different conditions of aeration in a medium containing 2% or 6% corn steep. At both concentrations, excessive aeration decreased enzyme production. In the medium with 2% corn steep, L-asparaginase activity began to decline as soon as the oxygen absorption exceeded 0.22 mmol O2 l–1 min–1, and when the oxygen absorption rate was 1.26 mmol O2 l–1 min–1, enzyme activity reached only about 5% of maximum. In the medium with 6% corn steep, a decline of L-asperaginase activity did not appear until the oxygen absorption rate value exceeded 0.54 mmol O2 l–1 min–1, at the oxygen absorption rate of 1.26 mmol O2 l–1 min–1, the enzyme activity still reached about 50% of maximum. 相似文献
20.
R. Bucala 《Redox report : communications in free radical research》2013,18(5):291-307
AbstractThe kinetics and mechanistic aspects of the riboflavin-photosensitised oxidation of the topically administrable ophthalmic drugs Timolol (Tim) and Pindolol (Pin) were investigated in water–MeOH (9:1, v/v) solution employing light of wavelength > 400 nm. riboflavin, belonging to the vitamin B2 complex, is a known human endogenous photosensitiser. The irradiation of riboflavin in the presence of ophthalmic drugs triggers a complex picture of competitive reactions which produces the photodegradation of both the drugs and the pigment itself. The mechanism was elucidated employing stationary photolysis, polarographic detection of dissolved oxygen, stationary and time-resolved fluorescence spectroscopy, and laser flash photolysis. Ophthalmic drugs quench riboflavin-excited singlet and triplet states. From the quenching of excited triplet riboflavin, the semireduced form of the pigment is generated, through an electron transfer process from the drug, with the subsequent production of superoxide anion radical (O2?–) by reaction with dissolved molecular oxygen. Through the interaction of dissolved oxygen with excited triplet riboflavin, the species singlet oxygen (O2(1Δg)) is also generated to a lesser extent. Both O2?– and O2(1Δg) induce photodegradation of ophthalmic drugs, Tim being ~3-fold more easily photooxidisable than Pin, as estimated by oxygen consumption experiments. 相似文献