共查询到20条相似文献,搜索用时 15 毫秒
1.
Furuike S Adachi K Sakaki N Shimo-Kon R Itoh H Muneyuki E Yoshida M Kinosita K 《Biophysical journal》2008,95(2):761-770
F1-ATPase, a water-soluble portion of the enzyme ATP synthase, is a rotary molecular motor driven by ATP hydrolysis. To learn how the kinetics of rotation are regulated, we have investigated the rotational characteristics of a thermophilic F1-ATPase over the temperature range 4-50°C by attaching a polystyrene bead (or bead duplex) to the rotor subunit and observing its rotation under a microscope. The apparent rate of ATP binding estimated at low ATP concentrations increased from 1.2 × 106 M−1 s−1 at 4°C to 4.3 × 107 M−1 s−1 at 40°C, whereas the torque estimated at 2 mM ATP remained around 40 pN·nm over 4-50°C. The rotation was stepwise at 4°C, even at the saturating ATP concentration of 2 mM, indicating the presence of a hitherto unresolved rate-limiting reaction that occurs at ATP-waiting angles. We also measured the ATP hydrolysis activity in bulk solution at 4-65°C. F1-ATPase tends to be inactivated by binding ADP tightly. Both the inactivation and reactivation rates were found to rise sharply with temperature, and above 30°C, equilibrium between the active and inactive forms was reached within 2 s, the majority being inactive. Rapid inactivation at high temperatures is consistent with the physiological role of this enzyme, ATP synthesis, in the thermophile. 相似文献
2.
Tadashi Matsubara Sou Nagasoe Yasuhiro Yamasaki Tomoyuki Shikata Yohei Shimasaki Yuji Oshima Tsuneo Honjo 《Journal of experimental marine biology and ecology》2007,342(2):226-230
The effects of temperature, salinity, and irradiance on the growth of the dinoflagellate Akashiwo sanguinea were examined in the laboratory. The irradiance at the light compensation point (I0) was 14.40 μmol m− 2 s− 1 and the irradiance at growth saturation (Is) was 114 μmol m− 2 s− 1. We exposed A. sanguinea to 48 combinations of temperature (5-30 °C) and salinity (5-40) under saturating irradiance; it exhibited its maximum growth rate of 1.13 divisions/day at a combination of 25 °C and salinity of 20. A. sanguinea was able to grow at temperatures from 10 to 30 °C and salinities from 10 to 40. This study revealed that A. sanguinea was a eurythermal and euryhaline organism; in Japan it should have formed blooms in early summer, when salinity was relatively low. In addition, it was noteworthy that A. sanguinea had markedly cold-durability, retaining the motile form of vegetative cells for more than 50 days at 5 °C and at salinities of 25-30. 相似文献
3.
Ahmed I. Hanafy 《Inorganica chimica acta》2005,358(4):1247-1252
The copper (II) complex of a simple pyridine- and amide-containing copolymer serves as an effective catalyst for heterogeneous hydrolysis of the prototypical phosphodiester substrate bis(p-nitrophenyl)phosphate at pH 8.0 and 25 °C. The catalysis has a first-order rate constant of kcat = 8.3 × 10−6 s−1, corresponding to a catalytic proficiency of 75-thousand folds relative to the uncatalyzed hydrolysis with a rate constant of k0 = 1.1 × 10−10 s−1 in aqueous buffer solution at pH 8.0. This observation suggests that polymers can be designed to include various functional groups feasible for effective metal-centered catalysis of phosphodiester hydrolysis. 相似文献
4.
T.T.T. Huynh A.J.A. Aarnink M.J.W. Heetkamp M.W.A. Verstegen B. Kemp 《Journal of thermal biology》2007
The effects of relative humidity and ambient temperature on evaporative heat loss were studied in 12 trials each with a group of 10 gilts with an initial BW of 61.7 kg (58.0–65.5 kg). The ambient temperature inside a respiration chamber was increased by 2 °C d−1 starting at 16 °C and ending at 32 °C. Relative humidity was set at 50%, 65% or 80% and remained constant within each trial. The animals had free access to feed and water. Skin temperature (SkinT), total heat production (HP), evaporative heat loss (EvapH), respiration rate (RR), and wallowing of the animals were recorded. SkinT was lowest at 80% relative humidity (P<0.05). For each degree Celsius rise in SkinT, wallowing increased by 0.19% (P<0.05). For each degree Celsius rise in ambient temperature, total HP decreased by 115 kJ pig−1 d−1 and EvapH increased by 290 kJ pig−1 d−1 (P<0.05). It was concluded that under constant high ambient temperature and relative humidity, the pigs clearly employ respiratory evaporation to lose heat. Wallowing showed the importance of skin EvapH with higher temperatures, especially at high relative humidity. This study shows the importance of evaporative cooling from the skin. The implication is that pigs at high ambient temperatures, especially in combination with a high relative humidity, should be able to wet themselves. For animal welfare and environmental reasons, it is important that they are able to wet their skin. 相似文献
5.
In order for cryopreservation to become a practical tool for aquaculture, optimized protocols must be developed for each species and cell type. Knowledge of a cell’s osmotic tolerance and membrane permeability characteristics can assist in optimized protocol development. In this study, these characteristics were determined for Pacific oyster oocytes and modified methods for loading and unloading ethylene glycol (EG) were tested. Oocytes were found to behave as ideal osmometers and their osmotically inactive fraction (Vb) was calculated to be 0.48. Oocytes exposed to NaCl solutions of 0.6 to 2.3 Osm fertilized at rates equivalent to oocytes left in seawater. This corresponds to volume changes of +27.3 and −38.1 ± 1.2%. The permeability of the oocytes to water (Lp) was determined to be 3.8 ± 0.4 × 10−2, 5.7 ± 0.8 × 10−2, and 13.2 ± 1.3 × 10−2 μm min−1 atm−1, when measured at temperatures of 5, 10 and 20 °C. The respective EG permeability values (Ps) were 9.5 ± 0.1 × 10−5, 14.6 ± 1.2 × 10−5, and 41.7 ± 2.4 × 10−5 cm min−1. The activation energies for Lp and Ps were determined to be 14.5 and 17.5 kcal mol−1, respectively. Different models for EG loading and unloading from oocytes were developed and tested. Post-thaw fertilization did not differ significantly between a published step addition method and single step addition at 20 °C. This represents a considerable reduction in handling. The results of this study demonstrate that the cryobiological characteristics of a given cell type should be taken into account when developing cryopreservation methods. 相似文献
6.
This study reports temperature effects on paralarvae from a benthic octopus species, Octopus huttoni, found throughout New Zealand and temperate Australia. We quantified the thermal tolerance, thermal preference and temperature-dependent respiration rates in 1-5 days old paralarvae. Thermal stress (1 °C increase h−1) and thermal selection (∼10-24 °C vertical gradient) experiments were conducted with paralarvae reared for 4 days at 16 °C. In addition, measurement of oxygen consumption at 10, 15, 20 and 25 °C was made for paralarvae aged 1, 4 and 5 days using microrespirometry. Onset of spasms, rigour (CTmax) and mortality (upper lethal limit) occurred for 50% of experimental animals at, respectively, 26.0±0.2 °C, 27.8±0.2 °C and 31.4±0.1 °C. The upper, 23.1±0.2 °C, and lower, 15.0±1.7 °C, temperatures actively avoided by paralarvae correspond with the temperature range over which normal behaviours were observed in the thermal stress experiments. Over the temperature range of 10 °C-25 °C, respiration rates, standardized for an individual larva, increased with age, from 54.0 to 165.2 nmol larvae−1 h−1 in one-day old larvae to 40.1-99.4 nmol h−1 at five days. Older larvae showed a lesser response to increased temperature: the effect of increasing temperature from 20 to 25 °C (Q10) on 5 days old larvae (Q10=1.35) was lower when compared with the 1 day old larvae (Q10=1.68). The lower Q10 in older larvae may reflect age-related changes in metabolic processes or a greater scope of older larvae to respond to thermal stress such as by reducing activity. Collectively, our data indicate that temperatures >25 °C may be a critical temperature. Further studies on the population-level variation in thermal tolerance in this species are warranted to predict how continued increases in ocean temperature will limit O. huttoni at early larval stages across the range of this species. 相似文献
7.
Lasia spinosa seeds were not dormant at maturity in early spring. The most favorable temperatures for germination were between 25 and 30 °C, and final percentage and rate of germination decreased with an increase or decrease in temperature. When L. spinosa seeds were transferred to 25 °C, after 60 days at 10 °C (where none of the seeds germinated), final germination increased from 0% to 78%. Seeds germinated to high percentage both in light and in dark, although dark germination took more than twice as long as in the light. During desiccation of seeds at 15 °C and 45% relatively humidity, moisture loss decreased exponentially from 2.02 to 0.13 g H2O g−1 dry wt within 16 days, and only a few seeds (12%) survived 0.13 g H2O g−1 dry wt moisture content. Seeds stored at 0.58 g H2O g−1 dry wt moisture content at four constant temperatures (4, 10, 15, and −18 °C) for up to 6 months exhibited a well-defined trend of decreasing viability with decreasing temperature. Thus, we concluded that freshly harvested L. spinosa seeds are non-dormant and recalcitrant. Also, the seeds with 0.58 g H2O g−1 dry wt moisture content could be effectively stored for a few months between 10 and 15 °C although the most appropriate temperature for wet storage appears to be 10 °C, as it is close to the minimum temperature for germination and so there will be less pre-sprouting compared to 15 °C. 相似文献
8.
Sin Yuin Yeo Mariska de Smet Sander Langereis Luce Vander Elst Robert N. Muller Holger Grüll 《生物化学与生物物理学报:生物膜》2014
Temperature-sensitive liposomes (TSLs) loaded with doxorubicin (Dox), and Magnetic Resonance Imaging contrast agents (CAs), either manganese (Mn2 +) or [Gd(HPDO3A)(H2O)], provide the advantage of drug delivery under MR image guidance. Encapsulated MRI CAs have low longitudinal relaxivity (r1) due to limited transmembrane water exchange. Upon triggered release at hyperthermic temperature, the r1 will increase and hence, provides a means to monitor drug distribution in situ. Here, the effects of encapsulated CAs on the phospholipid bilayer and the resulting change in r1 were investigated using MR titration studies and 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles. Our results show that Mn2 + interacted with the phospholipid bilayer of TSLs and consequently, reduced doxorubicin retention capability at 37 °C within the interior of the liposomes over time. Despite that, Mn2 +-phospholipid interaction resulted in higher r1 increase, from 5.1 ± 1.3 mM− 1 s− 1 before heating to 32.2 ± 3 mM− 1 s− 1 after heating at 60 MHz and 37 °C as compared to TSL(Gd,Dox) where the longitudinal relaxivities before and after heating were 1.2 ± 0.3 mM− 1 s− 1 and 4.4 ± 0.3 mM− 1 s− 1, respectively. Upon heating, Dox was released from TSL(Mn,Dox) and complexation of Mn2 + to Dox resulted in a similar Mn2 + release profile. From 25 to 38 °C, r1 of [Gd(HPDO3A)(H2O)] gradually increased due to increase transmembrane water exchange, while no Dox release was observed. From 38 °C, the release of [Gd(HPDO3A)(H2O)] and Dox was irreversible and the release profiles coincided. By understanding the non-covalent interactions between the MRI CAs and phospholipid bilayer, the properties of the paramagnetic TSLs can be tailored for MR guided drug delivery. 相似文献
9.
Astrid C. Wittmann Daniela Storch Klaus Anger Hans O. Pörtner Franz J. Sartoris 《Journal of experimental marine biology and ecology》2011,397(1):27-37
Marine brachyuran and anomuran crustaceans are completely absent from the extremely cold (− 1.8 °C) Antarctic continental shelf, but caridean shrimps are abundant. This has at least partly been attributed to low capacities for magnesium excretion in brachyuran and anomuran lithodid crabs ([Mg2+]HL = 20-50 mmol L− 1) compared to caridean shrimp species ([Mg2+]HL = 5-12 mmol L− 1). Magnesium has an anaesthetizing effect and reduces cold tolerance and activity of adult brachyuran crabs. We investigated whether the capacity for magnesium regulation is a factor that influences temperature-dependent activity of early ontogenetic stages of the Sub-Antarctic lithodid crab Paralomis granulosa. Ion composition (Na+, Mg2+, Ca2+, Cl−, SO42−) was measured in haemolymph withdrawn from larval stages, the first and second juvenile instars (crabs I and II) and adult males and females. Magnesium excretion improved during ontogeny, but haemolymph sulphate concentration was lowest in the zoeal stages. Neither haemolymph magnesium concentrations nor Ca2+:Mg2+ ratios paralleled activity levels of the life stages. Long-term (3 week) cold exposure of crab I to 1 °C caused a significant rise of haemolymph sulphate concentration and a decrease in magnesium and calcium concentrations compared to control temperature (9 °C). Spontaneous swimming activity of the zoeal stages was determined at 1, 4 and 9 °C in natural sea water (NSW, [Mg2+] = 51 mmol L− 1) and in sea water enriched with magnesium (NSW + Mg2+, [Mg2+] = 97 mmol L− 1). It declined significantly with temperature but only insignificantly with increased magnesium concentration. Spontaneous velocities were low, reflecting the demersal life style of the zoeae. Heart rate, scaphognathite beat rate and forced swimming activity (maxilliped beat rate, zoea I) or antennule beat rate (crab I) were investigated in response to acute temperature change (9, 6, 3, 1, − 1 °C) in NSW or NSW + Mg2+. High magnesium concentration reduced heart rates in both stages. The temperature-frequency curve of the maxilliped beat (maximum: 9.6 beats s− 1 at 6.6 °C in NSW) of zoea I was depressed and shifted towards warmer temperatures by 2 °C in NSW + Mg2+, but antennule beat rate of crab I was not affected. Magnesium may therefore influence cold tolerance of highly active larvae, but it remains questionable whether the slow-moving lithodid crabs with demersal larvae would benefit from an enhanced magnesium excretion in nature. 相似文献
10.
The reaction of with Co(dmgBF2)2(H2O)2 in 1.0 M HClO4/LiClO4 was found to be first-order in both reactants and the [H+] dependence of the second-order rate constant is given by k2obs = b/[H+], b at 25 °C is 9.23 ± 0.14 × 102 s−1. The [H+] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as Ka = 9.5 × 10−3 M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH2)5OH2+/+ were used to estimate an electron self-exchange rate constant of k22 = 1.7 × 10−4 M−1 s−1 for . 相似文献
11.
Xinting Yuan John H. Horner Leslie W.-M. Fung 《Journal of inorganic biochemistry》2010,104(11):1156-908
Oxidation of the heme-thiolate enzyme chloroperoxidase (CPO) from Caldariomyces fumago with peroxynitrite (PN) gave the Compound II intermediate, which was photo-oxidized with 365 nm light to give a reactive oxidizing species. Cryo-solvents at pH ≈ 6 were employed, and reactions were conducted at temperatures as low as − 50 °C. The activity of CPO as evaluated by the chlorodimedone assay was unaltered by treatment with PN or by production of the oxidizing transient and subsequent reaction with styrene. EPR spectra at 77 K gave the amount of ferric protein at each stage in the reaction sequence. The PN oxidation step gave a 6:1 mixture of Compound II and ferric CPO, the photolysis step gave an approximate 1:1 mixture of active oxidant and ferric CPO, and the final mixture after reaction with excess styrene contained ferric CPO in 80% yield. In single turnover reactions at − 50 °C, styrene was oxidized to styrene oxide in high yield. Kinetic studies of styrene oxidation at − 50 °C displayed saturation kinetics with an equilibrium constant for formation of the complex of Kbind = 3.8 × 104 M− 1 and an oxidation rate constant of kox = 0.30 s− 1. UV-Visible spectra of mixtures formed in the photo-oxidation sequence at ca. − 50 °C did not contain the signature Q-band absorbance at 690 nm ascribed to CPO Compound I prepared by chemical oxidation of the enzyme, indicating that different species were formed in the chemical oxidation and the photo-oxidation sequence. 相似文献
12.
The glycolytic enzyme triose phosphate isomerase from Schistosoma mansoni is a potential target for drugs and vaccines. Molecular modelling of the enzyme predicted that a Ser-Ala-Asp motif which is believed to be a helminth-specific epitope is exposed. The enzyme is dimeric (as judged by gel filtration and cross-linking), resistant to proteolysis and highly stable to thermal denaturation (melting temperature of 82.0 °C). The steady-state kinetic parameters are high (Km for dihydroxyacetone phosphate is 0.51 mM; Km for glyceraldehyde 3-phosphate is 1.1 mM; kcat for dihydroxyacetone phosphate is 7800 s−1 and kcat for glyceraldehyde 3-phosphate is 6.9 s−1). 相似文献
13.
The folding mechanism and stability of dimeric formate dehydrogenase from Candida methylica was analysed by exposure to denaturing agents and to heat. Equilibrium denaturation data yielded a dissociation constant of about 10−13 M for assembly of the protein from unfolded chains and the kinetics of refolding and unfolding revealed that the overall process comprises two steps. In the first step a marginally stable folded monomeric state is formed at a rate (k1) of about 2 × 10−3 s−1 (by deduction k−1 is about10−4 s−1) and assembles into the active dimeric state with a bimolecular rate constant (k2) of about 2 × 104 M−1 s−1. The rate of dissociation of the dimeric state in physiological conditions is extremely slow (k−2 ∼ 3 × 10−7 s−1). 相似文献
14.
Jutta Vlasits Paul G. FurtmüllerChrista Jakopitsch Marcel ZamockyChristian Obinger 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(4):799-805
Catalase-peroxidases (KatGs) are unique bifunctional heme peroxidases that exhibit peroxidase and substantial catalase activities. Nevertheless, the reaction pathway of hydrogen peroxide dismutation, including the electronic structure of the redox intermediate that actually oxidizes H2O2, is not clearly defined. Several mutant proteins with diminished overall catalase but wild-type-like peroxidase activity have been described in the last years. However, understanding of decrease in overall catalatic activity needs discrimination between reduction and oxidation reactions of hydrogen peroxide. Here, by using sequential-mixing stopped-flow spectroscopy, we have investigated the kinetics of the transition of KatG compound I (produced by peroxoacetic acid) to its ferric state by trapping the latter as cyanide complex. Apparent bimolecular rate constants (pH 6.5, 20 °C) for wild-type KatG and the variants Trp122Phe (lacks KatG-typical distal adduct), Asp152Ser (controls substrate access to the heme cavity) and Glu253Gln (channel entrance) are reported to be 1.2 × 104 M− 1 s− 1, 30 M− 1 s− 1, 3.4 × 103 M− 1 s− 1, and 8.6 × 103 M− 1 s− 1, respectively. These findings are discussed with respect to steady-state kinetic data and proposed reaction mechanism(s) for KatG. Assets and drawbacks of the presented method are discussed. 相似文献
15.
Robert Tuba 《Inorganica chimica acta》2005,358(13):4081-4085
Kinetics of the reaction of octacarbonyl dicobalt with ethyl diazoacetate leading to [μ2-{ethoxycarbonyl(methylene)}-μ2-(carbonyl)-bis(tricarbonyl-cobalt)] (Co-Co) (1), dinitrogen, and carbon monoxide were investigated at 10 °C in heptane solution. The initial rate of the reaction was measured by following both the gas evolution and the decrease of the octacarbonyl dicobalt concentration. The rate is first order with respect to octacarbonyl dicobalt and a complex order with respect to ethyl diazoacetate and carbon monoxide depending on the ratio of their concentrations. This is in accord with the formation of a heptacarbonyl dicobalt reactive intermediate (k1 (10 °C) = (1.22 ± 0.06) × 10−3 s−1) for which carbon monoxide and ethyl diazoacetate compete (k−1/k2 (10 °C) = 1.34 ± 0.07). 相似文献
16.
Neszta Ungvári 《Inorganica chimica acta》2009,362(4):1333-1630
In CH2Cl2 solution and under a carbon monoxide atmosphere the cobalt complexes [μ2-{ethoxycarbonyl(methylene)}-μ2-(carbonyl)-bis(triphenylphosphanedicarbonyl-cobalt) (Co-Co)] (4) and [μ2-{ethoxycarbonyl(methylene)}-μ2-(carbonyl)-(tricarbonyl-cobalt)-(triphenylphosphanedicarbonyl-cobalt) (Co-Co)] (3) are in equilibrium. The equilibrium constant K = [3][PPh3]/[4][CO] at 10 °C is 1.03 ± 0.11. The bridging and terminal CO ligands in complex 3 or 4 exchange with external 13CO simultaneously. In accord with that variable-temperature 13C NMR spectra reveal fluxional behavior for both complexes. The overall rate constant of 13CO-exchange for 3 at 10 °C is 17 × 10−3 s−1 and for 4 at 10 °C is 26 × 103 s−1. In the case of complex 4 the concentration of PPh3 has practically no influence on the rate of the 13CO-exchange reaction and on the rate of the reaction with CO. The coupling of the μ2-ethoxycarbonylcarbene ligand and one of the coordinated carbon monoxide is at least one order of magnitude slower than the 13CO-exchange reactions, and is faster in complex 4 than in complex 3. The partial pressure of carbon monoxide has practically no effect on the coupling reaction. 相似文献
17.
Typically, subzero permeability measurements are experimentally difficult and infrequently reported. Here we report an approach we have applied to mouse oocytes. Interrupted cooling involves rapidly cooling oocytes (50 °C/min) to an intermediate temperature above the intracellular nucleation zone, holding them for up to 40 min while they dehydrate, and then rapidly cooling them to −70 °C or below. If the intermediate holding temperature and holding time are well chosen, high post thaw survival of the oocytes is possible because the freezable water is removed during the hold. The length of time required for the exit of the freezable water allows the water permeability at that temperature to be determined. These experiments used 1.5 M ethylene glycol in PBS and included a transient hold of 2 min for equilibration at −10 °C, just below the extracellar ice formation temperature. We obtain an Lp = 1.8 × 10−3 μm min−1 atm−1 at −25 °C based on a hold time of 30 min yielding 80% survival and the premise that most of the freezable water is removed during the 30 min hold. If we assume that the water permeability is a continuous function of temperature and that its Ea changes at 0 °C, we obtain a subzero Ea of 21 kcal/mol; higher than the suprazero value of 14 kcal/mol. A number of assumptions are required for these water loss calculations and the resulting value of Lp can vary by up to a factor of 2, depending on the choices make. 相似文献
18.
A thermostable alkaline protease produced from Bacillus sp. JB 99 exhibited significant keratinolytic and dehairing activity. The enzyme was purified by ammonium sulphate precipitation followed by CM-cellulose and Sephadex G-100 chromatography and resulted in 13.6 fold purification with 23.8% of recovery. The specific activity of purified enzyme was 2989.6 U mg−l. Purified protease had a molecular weight of 29 kDa and appeared as a single band. Gelatin zymogram analysis also revealed a clear hydrolytic zone, which corresponded to the band obtained with SDS-PAGE. The optimum pH and temperature for the keratinolytic activity was pH 11.0 and 70 °C respectively and half life of protease was 70 °C for 4 h. N-terminal amino acid sequence of purified enzyme exhibited extensive homology with other thermostable alkaline proteases and inhibition by PMSF indicated serine type of protease. The Km and Vmax of protease for keratin substrate were 3.8 ± 0.5 mg ml−1 and 15.1 ± 1.6 ??m min−1 mg−1 and casein were 3.3 ± 0.4 mg ml−l and 15.6 ± 0.9 ??m min−1 mg−1 respectively. The enzyme efficiently dehaired buffalo and goat hide without damaging the collagen layer, which makes it a potential candidate for application in leather industry to avoid pollution problem associated with the use of chemicals in the industry. The enzyme also degraded chicken feathers in presence of reducing agent which can help poultry industry in management of keratin-rich waste and obtaining value added products. 相似文献
19.
Randy B. Stockbridge 《Bioorganic chemistry》2010,38(5):224-3642
Previous estimates of the rate of spontaneous cleavage of the glycosidic bond of adenosine were determined by extrapolating the rates of the acid- and base-catalyzed reactions to neutral pH. Here we show that cleavage also proceeds through a pH-independent mechanism. Rate constants were determined as a function of temperature at pH 7 and a linear Arrhenius plot was constructed. Uncatalyzed cleavage occurs with a rate constant of 3.7 × 10−12 s−1 at 25 °C, and the rate enhancement generated by the corresponding glycoside hydrolase is ∼5 × 1012-fold. 相似文献
20.
Su–Su Xia An–Wei Yu Li–Dan Zhao Hui–Ying Zhang Wei–Hong Zheng Jin–Song Liu 《Journal of thermal biology》2013
Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (Tb), metabolic rate (MR) and EWL at ambient temperatures (Ta) between 5 and 40 °C. Overall, we found that mean body temperature was 42.4 °C and average minimum thermal conductance (C) was 0.15 ml O2 g−1 h−1 °C−1 measured between 5 and 20 °C. The thermal neutral zone (TNZ) was 31.8–35.3 °C and BMR was 181.83 ml O2 h−1. Below the lower critical temperature, MR increased linearly with decreasing Ta according to the relationship: MR (ml O2 h−1)=266.59–2.66 Ta. At Tas above the upper critical temperature, MR increased with Ta according to the relationship: MR (ml O2 h−1)=−271.26+12.85 Ta. EWL increased with Ta according to the relationship: EWL (mg H2O h−1)=−19.16+12.64 Ta and exceeded metabolic water production at Ta>14.0 °C. The high Tb and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures. 相似文献