Concentrations Of Azide Research Articles

Electrochemical behaviour of Ti–6Al–4V alloy and Ti in azide and halide solutions

Electrochemical techniques including open circuit potential measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion and passivation behaviour of Ti–6Al–4V alloy in sodium azide (NaN 3) solutions compared to the behaviour of its pure base metal Ti. The results showed that increasing azide concentration increases the rate of corrosion ( i corr) and shifts negatively the rest potential ( E f), as well as decreases the spontaneous thickening rates of the inner and outer layers constituting the passive oxide film on each sample. These effects are more accentuated for the alloy than for the metal. Moreover, the electrical resistance ( R ox) and the relative thickness (1/ C ox) of the oxide films on the two samples exhibit an almost linear decrease vs. NaN 3 concentration. The results suggested that addition of Al and V to Ti, although improves its machinability, yet it decreases the performance of its surface oxide film to protect the degradation of the metal. The alloy was found to be more susceptible to corrosion than its base metal, since Ti expresses higher apparent activation energy ( E a ) for the corrosion process than Ti–6Al–4V. Electrochemical behaviour of Ti in azide medium was also compared with that in various halide solutions. It was found that Ti has a stronger propensity to form spontaneous passivating oxide layers in bromide more than in azide and other halide media, where the positive shift in the value of E f and the simultaneous increase in the oxide film resistance ( R ox) follow the sequence: Br − > N 3 - > Cl − > I − > F −.

Roles of different intermediate active species in the mineralization reactions of phenolic pollutants under a UV-A/C photo-Fenton process

The roles of different intermediate oxidative species, such as singlet oxygen, triplet oxygen, superoxide radical anions and hydroperoxy or hydroxyl radicals, were studied in the mineralization reactions of solutions containing a mixture of three phenolic compounds (namely gallic, p-coumaric and protocatechuic acids). The degradation process that was developed was a ferrioxalate-induced artificial ultraviolet (UV)-A/C photo-Fenton system. Reactions were carried out in an UV reactor consisting of two 50-W UV-C lamps and two 75-W UV-A lamps. The roles played by the oxidative active species in various stages of the process were determined by running the reaction in the presence of different scavenging agents. Analyses were conducted within a multivariate experimental design combined with neural networks that included the following variables: initial concentrations of tert-butyl alcohol, 1,4-benzoquinone, sodium azide and potassium iodide. The response function was the %TOC removal after 15 and 60min of reaction. Under optimal conditions (e.g., in the absence of scavenging agents), 88% TOC removal of the phenolic mixture could be achieved in 60min at 28°C. Superoxide radical anions and triplet oxygen were the main oxidants in earlier stages of the mineralization of this phenolic-mixture solution, whereas singlet oxygen, hydroxyl and hydroperoxy radicals played more significant roles in later stages. Tert-butyl alcohol was the most significant scavenger affecting inhibition of the mineralization reaction, as it trapped almost all of the intermediate active species.

Induced mutations in chickpea-morphological mutants

Seeds of two varieties (PUSA-212 and BG-256) of chickpea (Cicer arietinum L.) were treated with 0.03% concentration of hydrazine hydrate (HZ), methylmethane sulphonate (MMS) and sodium azide (SA) for 6 h. The M2 generation was grown from single plant M1 progeny seeds. Five morphological mutants (dwarf, bushy, one sided branch, narrow leaf and gigas) were isolated in M2 generation. Some of these mutants may be directly used in selection whereas some are useful in combination breeding programs.

Tethering Hydrophobic Peptides to Functionalized Self-Assembled Monolayers on Gold through Two Chemical Linkers Using the Huisgen Cycloaddition

Gold surfaces functionalized with an α-helical peptide have been generated by reacting an azide-terminated self-assembled monolayer with structured peptides containing two cyanophenylalanines through a Huisgen cycloaddition. Mixed monolayers of a reactive bromine-terminated thiol and inert alkane thiol were prepared at various concentrations of the Br-terminated moiety. These were reacted with sodium azide to form azide-terminated monolayers with controlled concentration of the reactive azide. These surfaces were studied through ellipsometry and X-ray photoelectron spectroscopy, which demonstrated that the concentration of the reactive azide group on the surface is controlled by the chemical conditions under which the monolayer is prepared. Grazing incident angle surface infrared spectroscopy (GRAS-IR) of the azide-terminated surface demonstrated that the azide is approximately perpendicular to the plane of the surface, as expected. These surfaces were then exposed to an α-helical peptide composed of alternating leucine and lysine residues, with two residues replaced with cyanophenylalanine to react with two neighboring surface-bound azide groups to bind the peptide to the surface through two covalent bonds. The yield of this reaction was quantified through monitoring the absorption of the azide group by GRAS-IR. Despite damage to the monolayer during the reaction, reaction yields of 80-98% were determined for optimized reaction conditions. Although the peptide retains its α-helical configuration under the reaction conditions, GRAS-IR analysis of the amide I and II modes of the surface-bound peptide showed that it is probably randomly oriented on the surface.

Mutagenic effectiveness and efficiency in varieties of sunflower (Helianthus annuus L.) by separate and combined treatment with gamma-rays and sodium azide

The effect of single treatment with gamma-rays, sodium azide and combination treatments of gammarays and sodium azide on seed germination, seedling survival, pollen fertility and seed set in sunflower (Helianthus annuus L.) M2 generation was studied in the varieties of USH-430 and SHSF-333. There was gradual decrease of seedling survival and pollen fertility with an increase in the dose of mutagen in both varieties. The percentage of lethality and achene sterility gradually increased with an increased dose. In USH-430 variety, the seed set percentage was significantly increased at 6kR, 4 mM and 6 kR + 6 mM, respectively. Mutagenic effectiveness decreased with an increased dose or concentration of gamma-rays and sodium azide in both varieties. In combined treatments, mutagenic effectiveness gradually increased with an increased dose. Mutagenic efficiency increased with an increased dose in case of gamma-irradiated seeds in both varieties. Mutagenic efficiency decreased gradually with an increased dose in both varieties. The linear correlation co-efficient was positive in case of gamma-rays and sodium azide separated, whereas in combined treatment, negative correlation was observed.

ChemInform Abstract: Role of Azide Concentration in Pulse Radiolysis Studies of Oxidation: 3,4-Dihydroxyphenylalanine.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Replacement of imidazoles by azide at an iron(III) porphyrin center: part 1 replacement of N-methylimidazole in bis-(N-methylimidazole)tetraphenylporphyrinato iron(III)

Addition of tetra-n-butylammonium azide to acetone solutions of the tetraphenylporphyrinato iron(III) complex [Fe(TPP)(MeIm)2]+ formed in situ from the reaction of N-methylimidazole and [Fe(TPP)N3] afforded equilibrium amounts of [Fe(TPP)(MeIm)2]+ and [Fe(TPP)(MeIm)N3]. Equilibrium experiments made using a range of known concentrations of added tetra-n-butylammonium azide and N-methylimidazole using stopped-flow apparatus gave an estimate of about 50 for the equilibrium constant for the formation of [Fe(TPP)(MeIm)N3] from the addition of azide to [Fe(TPP)(MeIm)2]+. Kinetic studies indicated that the substitution of azide ion by N-methylimidazole is a dissociative process, and the results were interpreted using a stationary state approach in which [Fe(TPP)(MeIm)]+ was the transient intermediate that discriminated in favor of the reaction with azide as opposed to the reaction with N-methylimidazole by about a factor of two. Loss of N-methylimidazole from [Fe(TPP)(MeIm)2]+ is at least 50 times faster than that from the product [Fe(TPP)(MeIm)N3]. Using calculated values of free azide concentrations from experimentally determined ion-pair formation constants led to success in rationalizing results obtained under different conditions.

Determination of the concentration of active sites and the catalytic rate constant of recombinant formate dehydrogenase from Glycine max

The analysis of a formate dehydrogenase (FDH) structure in the apo form and in a complex with nicotinamide (NAD+) and azide ion has shown a high probability of efficient fluorescence quenching during the formation of such a triple complex. The excitation and fluorescence spectra indicated that the enzyme fluorescence is determined by tryptophan residues. The dependence of FDH fluorescence quenching on the NAD+ and azide concentrations was studied. The obtained data were used to determine the concentration of active sites and the catalytic rate constant of recombinant FDH from Glycine max.

Effect of Limited Oxygen Supply on Coenzyme Q10 Production and Its Relation to Limited Electron Transfer and Oxidative Stress in Rhizobium radiobacter T6102

Coenzyme Q(10) (CoQ(10)) productions from Rhizobium radiobacter T6102 were monitored under various oxygen supply conditions by controlling the agitation speeds, aeration rates, and dissolved oxygen levels. As the results, the CoQ(10) production was enhanced by limited oxygen supply. To investigate whether the CoQ(10) production is associated with its physiological functions of electron carrier and antioxidant, the effects of sodium azide and hydrogen peroxide on the CoQ(10) production were studied, showing that the CoQ(10) contents were slightly enhanced with increasing sodium azide (up to 0.4 mM) and hydrogen peroxide (up to 10 microM) concentrations. These results suggest the plausible mechanism where the limited electron transfer stimulating the environments of limited oxygen supply and oxidative stress could accumulate the CoQ(10), providing the relationship between the CoQ(10) physiological functions and its regulation system.

Ligand Trapping by Cytochrome c Oxidase: IMPLICATIONS FOR GATING AT THE CATALYTIC CENTER

Cytochrome c oxidase is a member of the heme-copper family of oxygen reductases in which electron transfer is linked to the pumping of protons across the membrane. Neither the redox center(s) associated with proton pumping nor the pumping mechanism presumably common to all heme-copper oxidases has been established. A possible conformational coupling between the catalytic center (Fe(a3)(3+)-Cu(B)(2+)) and a protein site has been identified earlier from ligand binding studies, whereas a structural change initiated by azide binding to the protein has been proposed to facilitate the access of cyanide to the catalytic center of the oxidized bovine enzyme. Here we show that cytochrome oxidase pretreated with a low concentration of azide exhibits a significant increase in the apparent rate of cyanide binding relative to that of free enzyme. However, this increase in rate does not reflect a conformational change enhancing the rapid formation of a Fe(a3)(3+)-CN-Cu(B)(2+) complex. Instead the cyanide-induced transition of a preformed Fe(a3)(3+)-N(3)-Cu(B)(2+) to the ternary complex of Fe(a3)(3+)-N(3) Cu(B)(2+)-CN is the most likely reason for the observed acceleration. Significantly, the slow rate of azide release from the ternary complex indicates that cyanide ligated to Cu(B) blocks a channel between the catalytic site and the solvent. The results suggest that there is a pathway that originates at Cu(B) and that, during catalysis, ligands present at this copper center control access to the iron of heme a(3) from the bulk medium.

Sodium azide induced mutation of Actinomycetes I

Sodium azide was employed to generate mutants of actinomycetes from Mount Everest region, viz. Sagarmatha National Park, Jorsale, Kalapatthar and Namche. Individual isolates of actinomycetes were inoculated on Starch Casein Agar plates containing 10, 50 and 100 ppm of sodium azide. Depending on complete inhibition of their growth , actinomycete isolates were categorized as highly sensitive , moderately sensitive and tolerant, respectively. Out of a total of 38 actinomycetes isolates, two (5.3%) were highly sensitive, 23 (60.5%) moderately sensitive and 13 (34.2%) tolerant. A total of 21 mutants were generated by treating 8 of the 23 moderately sensitive actinomycetes with 20, 30 and 40 ppm (sublethal concentrations ) of sodium azide and analyzed morphologically and biochemically. All mutants like wild strains were able to hydrolyse starch, Tween 20 and casein and utilize fructose and lactose. All were urease and catalase positive , but were different from wild strains in colony color or texture or both. Altogether nine (43 % ) mutants having negative mutation in loci of utilization of galactose or mannose (loss-of-function LOF, single mutants ) , two LOF double mutants in utilization of both galactose and arabinose , one gain-of-function (GOF) single mutant having positive mutation in the loci of utilization of galactose, one GOF double mutant in utilization of mannose and galactose and five double mutants (25%) having GOF ( arabinose or sucrose ) as well as LOF (mannose or galactose or arabinose) were obtained. Key words : Mt. Everest, Sagarmatha, actinomycetes, sodium azide, mutation, LOF, GOF DOI: 10.3126/ijls.v3i0.2385

Analysis and optimization of copper-catalyzed azide-alkyne cycloaddition for bioconjugation.

Since its discovery in 2002, the copper-catalyzed azide-alkyne cycloaddition (CuAAC)[1] reaction—the most widely recognized example of click chemistry[2]—has been rapidly embraced for applications in myriad fields.[3] The attractiveness of this procedure (and its copper-free strained-alkyne variant[4]) stems from the selective reactivity of azides and alkynes only with each other. Because of the fragile nature and low concentrations at which biomolecules are often manipulated, bioconjugation presents significant challenges for any ligation methodology. Several different CuAAC procedures have been reported to address specific cases involving peptides, proteins, polynucleotides, and fixed cells, often with excellent results,[5] but also occasionally with somewhat less satisfying outcomes.[6] We describe here a generally applicable procedure that solves the most vexing click bioconjugation problems in our laboratory, and therefore should be of use in many other situations. The CuAAC reaction requires the copper catalyst, usually prepared with an appropriate chelating ligand,[7] to be maintained in the CuI oxidation state. Several years ago we developed a system featuring a sulfonated bathophenanthroline ligand,[8] which was optimized into a useful bioconjugation protocol.[9] A significant drawback was the catalyst’s acute oxygen sensitivity, requiring air-free techniques which can be difficult to execute when an inert-atmosphere glove box is unavailable or when sensitive biomolecules are used in small volumes of aqueous solution. We also introduced an electrochemical method to generate and protect catalytically active CuI–ligand species for CuAAC bioconjugation and synthetic coupling reactions with miminal effort to exclude air.[10] Under these conditions, no hydrogen peroxide was produced in the oxygen-scrubbing process, resulting in protein conjugates that were uncontaminated with oxidative byproducts. However, this solution is also practical only for the specialist with access to the proper equipment. Other protocols have employed copper(I) sources such as CuBr for labeling fixed cells[11] and synthesizing glycoproteins.[12] In these cases, the instability of CuI in air imposes a requirement for large excesses of Cu (greater than 4 mm) and ligand for efficient reactions, which raises concerns about protein damage or precipitation, plus the presence of residual metal after purification. The most convenient CuAAC procedure involves the use of an in situ reducing agent. Sodium ascorbate is the reductant of choice for CuAAC reactions in organic and materials synthesis, but is avoided in bioconjugation with a few exceptions.[13] Copper and sodium ascorbate have been shown to be detrimental to biological[14] and synthetic[15] polymers due to copper-mediated generation of reactive oxygen species.[16] Moreover, dehydroascorbate and other ascorbate byproducts can react with lysine amine and arginine guanidine groups, leading to covalent modification and potential aggregation of proteins.[6a,17] We hoped that solutions to these problems would allow ascorbate to be used in fast and efficient CuAAC reactions using micromolar concentration of copper in the presence of atmospheric oxygen. This has now been achieved, allowing demanding reactions to be performed with biomolecules of all types by the nonspecialist. For purposes of catalyst optimization and reaction screening, the fluorogenic coumarin azide 1 developed by Wang et al. has proven to be invaluable (Scheme 1).[18] The progress of cycloaddition reactions between mid-micromolar concentrations of azide and alkyne in aqueous buffers was followed by the increase in fluorescence at 470 nm upon formation of the triazole 2. Scheme 1 Top: Reaction used for screening CuAAC catalysts and conditions. Below: Accelerating ligand 3 and additive 4 used in these studies. DMSO=dimethylsulfoxide.

Convenient Headspace Gas Chromatographic Determination of Azide in Blood and Plasma

Azide in human blood and plasma samples was derivatized with propionic anhydride in a headspace vial without prior sample preparation. The reaction proceeds quickly at room temperature to form propionyl azide. A portion of the headspace was assayed by gas chromatography with a nitrogen-phosphorus detector. In the heated injector of the gas chromatograph, the propionyl azide undergoes thermal rearrangement, forming ethyl isocyanate, which is subsequently chromatographed and detected. Propionitrile was used as the internal standard. The method is linear to at least 20 microg/mL. Limit of quantitation was 0.04 microg/mL, and the within-run coefficient of variation was 5.6% at 1 microg/mL. There was no interference from cyanide. A fatality report in which blood and plasma azide concentrations from a 59-year-old man were monitored for 24 h following the ingestion of an unknown amount of sodium azide is presented. The patient became critically ill after his self-inflicted sodium azide ingestion. He was intubated and treated with vasopressors and aggressive supportive care, including extracorporeal membrane oxygenation therapy, in the intensive care facility but died from neurological brain damage secondary to anoxia. On admission, 1.4 h after ingestion, his azide level was 5.6 microg/mL (blood); shortly thereafter, it had risen to 13.7 microg/mL (plasma) and, subsequently, was projected to have been eliminated by 16.7 h. No azide was detected in the postmortem blood and vitreous humor.

Synthesis, X-ray crystallographic characterization, and electronic structure studies of a di-azide iron(III) complex: implications for the azide adducts of iron(III) superoxide dismutase.

We have synthesized and characterized, using X-ray crystallographic, spectroscopic, and computational techniques, a six-coordinate diazide Fe (3+) complex, LFe(N 3) 2 (where L is the tetradentate ligand 7-diisopropyl-1,4,7-triazacyclononane-1-acetic acid), that serves as a model of the azide adducts of Fe (3+) superoxide dismutase (Fe (3+)SOD). While previous spectroscopic studies revealed that two distinct azide-bound Fe (3+)SOD species can be obtained at cryogenic temperatures depending on protein and azide concentrations, the number of azide ligands coordinated to the Fe (3+) ion in each species has been the subject of some controversy. In the case of LFe(N 3) 2, the electronic absorption and magnetic circular dichroism spectra are dominated by two broad features centered at 21 500 cm (-1) (approximately 4000 M (-1) cm (-1)) and approximately 30 300 cm (-1) (approximately 7400 M (-1) cm (-1)) attributed to N3 (-) --> Fe (3+) charge transfer (CT) transitions. A normal coordinate analysis of resonance Raman (RR) data obtained for LFe(N 3) 2 indicates that the vibrational features at 363 and 403 cm (-1) correspond to the Fe-N 3 stretching modes (nu Fe-N3) associated with the two different azide ligands and yields Fe-N 3 force constants of 1.170 and 1.275 mdyne/A, respectively. RR excitation profile data obtained with laser excitation between 16,000 and 22,000 cm (-1) reveal that the nu Fe-N3 modes at 363 and 403 cm (-1) are preferentially enhanced upon excitation in resonance with the N 3 (-) --> Fe (3+) CT transitions at lower and higher energies, respectively. Consistent with this result, density functional theory electronic structure calculations predict a larger stabilization of the molecular orbitals of the more strongly bound azide due to increased sigma-symmetry orbital overlap with the Fe 3d orbitals, thus yielding higher N 3 (-) --> Fe (3+) CT transition energies. Comparison of our data obtained for LFe(N 3) 2 with those reported previously for the two azide adducts of Fe (3+)SOD provides compelling evidence that a single azide is coordinated to the Fe (3+) center in each protein species.

Parabolic effect in sodium azide mutagenesis in barley*

In order to study the influence of sodium azide concentration on its mutagenic effect, treatments with this chemical (0, 1X10-4 5X10-4 1X10-3 5X10-3 M, pH 6, 20 h.) were applied to seeds of the two-row barley variety Malteria Heda and its double-mutant MC 90. In both genotypes the highest mutagenic effect was observed in the intermediate azide concentrations. The plotted data described a second degree parabole in relation to the azide molarity. The parabolic effect was presented in both forms of recording (chlorophyll mutations/ M1 spikes, and chlorophyll mutants/ M2 seedlings), and it was also found in ovule sterility. On the other hand, the results in physiological vitality, chromosome damage and survival of M1 mature plants were similar to or slightly different from those of the untreated controls.

Seed Yield is not Impaired by Chromosome Stickiness in Sodium Azide Treated Trigonella foenum-graecum

Partial or complete stickiness of chromosomes and disorientation of spindle were the major anomalies observed in meiocytes of Trigonella plants raised from seeds treated with different concentration of sodium azide for three durations. Other aberrations were unequal separation, non synchronous division, bridge, laggard, stray etc. The pollen fertility and yield showed an increase over control despite the high frequency of stickiness and spindle disorientation. Yield was positively correlated with stickiness, indicating a balancing/regulatory effect of stickiness at the time of gamete formation.

E-NTPDases and ecto-5′-nucleotidase expression profile in rat heart left ventricle and the extracellular nucleotide hydrolysis by their nerve terminal endings

In this study, we have identified the E-NTPDase family members and ecto-5′-nucleotidase/CD73 in rat heart left ventricle. Moreover, we characterize the biochemical properties and enzyme activities from synaptosomes of the nerve terminal endings of heart left ventricle. We observe divalent cation-dependent enzymes that presented optimum pH of 8.0 for ATP and ADP hydrolysis, and 9.5 for AMP hydrolysis. The apparent K M values are 40 μM, 90 μM and 39 μM and apparent V max values are 537, 219 and 111 nmol Pi released/min/mg of protein for ATP, ADP and AMP hydrolysis, respectively. Ouabain, orthovanadate, NEM, lanthanum and levamisole do not affect ATP and ADP hydrolysis in rat cardiac synaptosomes. Oligomycin (2 μg/mL) and sodium azide (0.1 mM), both mitochondrial ATPase inhibitors, inhibit only the ATP hydrolysis. High concentrations of sodium azide and gadolinium chloride show an inhibition on both, ATP and ADP hydrolysis. Suramin inhibit more strongly ATP hydrolysis than ADP hydrolysis whereas Evans blue almost abolish both hydrolysis. AMP hydrolysis is not affected by levamisole and tetramisole, whereas 0.1 mM ammonium molybdate practically abolish the ecto-5′-nucleotidase activity. RT-PCR analysis from left ventricle tissue demonstrate different levels of expression of Entpd1 ( Cd39), Entpd2 ( Cd39L1), Entpd3 ( Cd39L3), Entpd5 ( Cd39L4) Entpd6, ( Cd39L2) and 5′-NT/CD73. By quantitative real-time PCR we identify the Entpd2 as the enzyme with the highest expression in rat left ventricle. Our results contribute to the understanding about the control of the extracellular nucleotide levels in and cardiac system.

Mitochondrial Swelling Impairs the Transport of Organelles in Cerebellar Granule Neurons

Organelle transport in neuronal processes is central to the organization, developmental fate, and functions of neurons. Organelles must be transported through the slender, highly branched neuronal processes, making the axonal transport vulnerable to any perturbation. However, some intracellular structures like mitochondria are able to considerably modify their volume. We therefore hypothesized that swollen mitochondria could impair the traffic of other organelles in neurite shafts. To test this hypothesis, we have investigated the effects of mitochondrial swellers on the organelle traffic. Our data demonstrate that treatment of neurons with potassium ionophore valinomycin led to the fast time-dependent inhibition of organelle movement in cerebellar granule neurons. Similar inhibition was observed in neurons treated with the inhibitors of the mitochondrial respiratory chain, sodium azide and antimycin, which also induced swelling. No decrease in the motility of organelles was observed in cultures treated with inhibitors of ATP production or transport, oligomycin or bongkrekic acid, suggesting that inhibition of the ATP-generating activity itself without swelling does not affect the motility of organelles. The effect of swellers on the traffic was more important in thin processes, thus indicating the role of steric hindrance of swollen mitochondria. We propose that the size and morphology of the transported cargo is also relevant for seamless axonal transport and speculate that mitochondrial swelling could be one of the reasons for impaired organelle transport in neuronal processes.

A Comparative Study on Axial Coordination and Ligand Binding in Ferric Mini Myoglobin and Horse Heart Myoglobin

The absorption and resonance Raman spectra and the azide binding kinetics of ferric horse heart myoglobin (Mb) and mini myoglobin (a chemically truncated form of horse heart Mb containing residues 32–139) have been compared. The steady-state spectra show that an additional six-coordinated low-spin form (not present in entire horse heart Mb, which is purely six-coordinated high spin) predominates in mini Mb. The distal histidine is possibly the sixth ligand in this species. The presence of two species corresponds to a kinetic biphasicity for mini Mb that is not observed for horse heart Mb. Azide binds to horse heart Mb much more slowly than to sperm whale Mb. This difference may result from a sterically hindered distal pocket in horse heart Mb. In both cases, the rate constants level off at high azide concentrations, implying the existence of a rate-limiting step (likely referable to the dissociation of the axial sixth ligand). The faster rate constant of mini Mb is similar to that of sperm whale Mb, whereas the slower one is similar to that of entire horse heart Mb.

Ontogenic changes in tolerance to hypoxia and energy metabolism of larval and juvenile Japanese flounder Paralichthys olivaceus

Changes in tolerances to hypoxia and sodium azide, an indicator of cellular respiration, and activities of various energy metabolism-related chemical components were studied in Japanese flounder Paralichthys olivaceus during its early life stages from 3.5 to 20.5 mm in total length (TL). They showed flexion stage around 10.4 mm TL. Lethal levels of hypoxia increased with growth from 3.5 to 8 mm total TL, and the levels remained high in larvae, until 10.4 mm TL, decreased significantly thereafter. The 50% lethal concentration of sodium azide temporarily increased at 4.5 mm TL, diminished drastically between 4.5 and 10.4 mm TL, and then increased again in post-flexion larvae. Cytochrome c oxidase activity was highest in larvae around flexion, at 10.4 mm TL, and subsequently decreased. In post-flexion larvae at 13.0 mm TL, lactate dehydrogenase (LDH) and creatine kinase activities increased; LDH activity decreased at the juvenile stage. The adenosine triphosphate content and energy charge in fish were consistently higher in the larval stage than in the juvenile stage. These results indicated that, from just before flexion to the post-flexion stage, the energy metabolism of larvae is higher due to activated aerobic and subsequent anaerobic metabolism for metamorphosis; as a consequence, hypoxia tolerance in fish is the lowest during the increase of aerobic metabolism just before and around flexion.