Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise

The anion nitrate—abundant in our diet—has recently emerged as a major pool of nitric oxide (NO) synthase-independent NO production. Nitrate is reduced stepwise in vivo to nitrite and then NO and possibly other bioactive nitrogen oxides. This reductive pathway is enhanced during low oxygen tension and acidosis. A recent study shows a reduction in oxygen consumption during submaximal exercise attributable to dietary nitrate. We went on to study the effects of dietary nitrate on various physiological and biochemical parameters during maximal exercise. Nine healthy, nonsmoking volunteers (age 30 ± 2.3 years, VO_2max 3.72 ± 0.33 L/min) participated in this study, which had a randomized, double-blind crossover design. Subjects received dietary supplementation with sodium nitrate (0.1 mmol/kg/day) or placebo (NaCl) for 2 days before the test. This dose corresponds to the amount found in 100–300 g of a nitrate-rich vegetable such as spinach or beetroot. The maximal exercise tests consisted of an incremental exercise to exhaustion with combined arm and leg cranking on two separate ergometers. Dietary nitrate reduced VO_2max from 3.72 ± 0.33 to 3.62 ± 0.31 L/min, P < 0.05. Despite the reduction in VO_2max the time to exhaustion trended to an increase after nitrate supplementation (524 ± 31 vs 563 ± 30 s, P = 0.13). There was a correlation between the change in time to exhaustion and the change in VO_2max (R² = 0.47, P = 0.04). A moderate dietary dose of nitrate significantly reduces VO_2max during maximal exercise using a large active muscle mass. This reduction occurred with a trend toward increased time to exhaustion implying that two separate mechanisms are involved: one that reduces VO_2max and another that improves the energetic function of the working muscles.     

Muscle fibre conduction velocity and cardiorespiratory response during incremental cycling exercise in young and older individuals with different training status

We investigated the effect of ageing and training on muscle fibre conduction velocity (MFCV) and cardiorespiratory response during incremental cycling exercise. Eight young (YT; 24 ± 5 yrs) and eight older (OT; 64 ± 3 yrs) cyclists, together with eight young (YU; 27 ± 4 yrs) and eight older (OU; 63 ± 2 yrs) untrained individuals underwent to an incremental maximal test on a cycle ergometer. Ventilatory threshold (VT), respiratory compensation point (RCP) and maximal oxygen uptake (VO₂max) were identified and MFCV recorded from the vastus lateralis muscle using surface electromyography with linear arrays electrodes.In YT MFCV increased with the exercise intensity, reaching a peak of 4.99 ± 1.02 [m/s] at VT. Thereafter, and up to VO₂max, MFCV declined. In YU MFCV showed a similar trend although the peak [4.55 ± 0.53 m/s] was observed, at 75% of VO₂max an intensity higher than VT (66% of VO₂max). In both YT and YU MFCV did not decline until RPC, which occurred at 78% VO₂max in YU and at 92% VO₂max (P < 0.01) in YT. Differently from young individuals, MFCV in older subjects did not increase with exercise intensity. Moreover, maximal MFCV in OU was significantly lower [3.53 ± 0.40 m/s;] than that of YT (P < 0.005) and YU (P < 0.05).The present study shows that, especially in young individuals, MFCV reflects cardiorespiratory response during incremental dynamic cyclic exercise and hence can be used to investigate motor unit recruitment strategies.     

Relationship between ventilatory threshold and muscle fiber conduction velocity responses in trained cyclists

The relationship between surface electromyography (SEMG) amplitude and the ventilatory threshold has been extensively studied. However, previous studies of muscle fiber conduction velocity (MFCV) are scarce and present insufficient evidence concerning the relationship between MFCV and metabolic responses during cycling. Based on that fact, the purpose of this study is twofold: (1) to investigate the existence of a MFCV threshold (MFCVT) during cycling and (2) to verify if this possible breakpoint is correlated with the ventilatory threshold (VT) and the SEMG threshold (SEMGT). Eight trained male cyclists (age 36.0 ± 9.7 years) performed an incremental cycling test with initial workload of 150 W gradually incremented by 20 W min^?1 until the exhaustion. Gas analyses were conducted using a breath-by-breath open-circuit spirometry and SEMG were registered from vastus lateralis in each pedaling cycle with a linear array of electrodes. A bi-segmental linear regression computer algorithm was used to estimate VT, MFCVT and SEMGT respectively in the carbon dioxide production (VCO₂), MFCV and electromyography root mean square (EMG RMS) curves. The one way ANOVA for repeated measures did not reveal any significant difference among VT (77.1 ± 7.5% of VO₂max), MFCVT (80.3 ± 10.4% of VO₂max) and SEMGT (81.9 ± 11.7% of VO₂max). The Bland and Altman procedure confirmed a good concordance between SEMGT and VT (Bias = 5.5 of %VO₂max) as well as MFCVT and VT (Bias = 5.2 of %VO₂max). The present findings suggest that muscle fiber conduction velocity threshold is a valid and reliable non-invasive tool to obtain information about ventilatory threshold in trained cyclists.     

The effects of feeding on the swimming performance and metabolic response of juvenile southern catfish,Silurus meridionalis,acclimated at different temperatures

To test whether the effects of feeding on swimming performance vary with acclimation temperature in juvenile southern catfish (Silurus meridionalis), we investigated the specific dynamic action (SDA) and swimming performance of fasting and feeding fish at acclimation temperatures of 15, 21, 27, and 33 °C. Feeding had no effect on the critical swimming speeding (U_crit) of fish acclimated at 15 °C (p = 0.66), whereas it elicited a 12.04, 18.70, and 20.98% decrease in U_crit for fish acclimated at 21, 27 and 33 °C, respectively (p < 0.05). Both the maximal postprandial oxygen consumption rate (VO_2peak) and the active metabolic rate (VO_2active, maximal aerobic sustainable metabolic rate of fasting fish) increased significantly with temperature (p < 0.05). The postprandial maximum oxygen consumption rates during swimming (VO_2max) were higher than the VO_2active of fasting fish at all temperature groups (p < 0.05). The VO_2max increased with increasing temperature, but the relative residual metabolic scope (VO_2max? VO_2peak) during swimming decreased with increasing in temperature. The present study showed that the impairment of postprandial swimming performance increased with increasing temperature due to the unparalleled changes in the catfish's central cardio-respiratory, peripheral digestive and locomotory capacities. The different metabolic strategies of juvenile southern catfish at different temperatures may relate to changes in oxygen demand, imbalances in ion fluxes and dissolved oxygen levels with changes in temperature.     

Human mitochondrial haplogroup H: The highest VO2max consumer – Is it a paradox?

Mitochondrial background has been demonstrated to influence maximal oxygen uptake (VO_2max, in mL kg^?1 min^?1), but this genetic influence can be compensated for by regular exercise. A positive correlation among electron transport chain (ETC) coupling, ATP and reactive oxygen species (ROS) production has been established, and mitochondrial variants have been reported to show differences in their ETC performance. In this study, we examined in detail the VO_2max differences found among mitochondrial haplogroups. We recruited 81 healthy male Spanish Caucasian individuals and determined their mitochondrial haplogroup. Their VO_2max was determined using incremental cycling exercise (ICE). VO_2max was lower in J than in non-J haplogroup individuals (P = 0.04). The H haplogroup was responsible for this difference (VO_2max; J vs. H; P = 0.008) and this group also had significantly higher mitochondrial oxidative damage (mtOD) than the J haplogroup (P = 0.04). In agreement with these results, VO_2max and mtOD were positively correlated (P = 0.01). Given that ROS production is the major contributor to mtOD and consumes four times more oxygen per electron than the ETC, our results strongly suggest that ROS production is responsible for the higher VO_2max found in the H variant. These findings not only contribute to a better understanding of the mechanisms underneath VO_2max, but also help to explain some reported associations between mitochondrial haplogroups and mtOD with longevity, sperm motility, premature aging and susceptibility to different pathologies.     

Biceps brachii myoelectric and oxygenation changes during static and sinusoidal isometric exercises

Surface myoelectric signal changes occurring during sustained isometric contractions have been extensively studied with quantitative surface electromyography (sEMG) and are described by means of some sEMG global variables in time and frequency domain (such as the median power spectral frequency). Recently, the possibility of studying local muscle O₂ saturation during exercise using non-invasive methods has been enhanced thanks to the use of near-infrared spectroscopy (NIRS). The purpose of this work was to combine NIRS and sEMG techniques to analyze the relationship between modifications of sEMG parameters and the underlying metabolic status of the exercising biceps brachii muscle. This relationship was tested under different isometric contraction modalities, namely static (ST) at 20, 40, 60 and 80%MVC and sinusoidal (SIN) at 40 ± 20 and 60 ± 20%MVC. Results clearly indicated the presence of an initial fast phase of muscle O₂ desaturation followed by a slow phase, regardless of the contraction modality. Moreover, the initial rate of muscle O₂ desaturation was related to the level of force output (R = 0.92), but it was independent on the contraction modality (p < 0.05). Similarly, changes in sEMG parameters were related to force level (Conduction Velocity-CV vs. Force: R = 0.87; sEMG Median Frequency-MDF vs. Force: R = 0.86). The high correlation found between CV-MDF and Tissue Oxygenation Index (TOI) slope (R = 0.73 and 0.72, respectively) suggests a strong relationship between NIRS and sEMG data. This study indicates that muscle O₂ demand during isometric contractions from low to high force levels is influenced by the type of active motor units and not from the type of isometric exercise modality.     

Quadriceps EMG frequency content following isometric lumbar extension exercise

A relationship exists between muscles of the lumbar spine and those of the lower extremity where the quadriceps become more inhibited after lumbar paraspinal. The purpose of this experiment was to compare surface electromyography (sEMG) total frequency content after lumbar paraspinal fatiguing exercise. Scope: 50 subjects performed fatiguing lumbar extension exercise indexed by downward shifts in median frequency calculated from lumbar paraspinal sEMG signal. Before and after each exercise set we recorded maximal, isometric knee extension torque and quadriceps central activation ratio (QI) using the superimposed burst technique while recording vastus lateralis sEMG. We calculated total frequency content of the sEMG signal (fEMG_TOTAL) as the area of the quadriceps sEMG frequency spectrum. Quadriceps fEMG_TOTAL decreased from baseline following the first and second exercise sets. There was no significant change in quadriceps sEMG median frequency among baseline and post-exercise measures. The change in fEMG_TOTAL was correlated with the change in QI following the first (r = ?0.41, P = 0.003) and second (r = ?0.32, P = 0.02) exercise sets. Conclusion: Quadriceps fEMG_TOTAL decreased following fatiguing lumbar extension exercise, in the absence of a significant change in quadriceps median frequency.     

Knee flexor strength and bicep femoris electromyographical activity is lower in previously strained hamstrings

The aim of this study was to determine if athletes with a history of hamstring strain injury display lower levels of surface EMG (sEMG) activity and median power frequency in the previously injured hamstring muscle during maximal voluntary contractions. Recreational athletes were recruited, 13 with a history of unilateral hamstring strain injury and 15 without prior injury. All athletes undertook isokinetic dynamometry testing of the knee flexors and sEMG assessment of the biceps femoris long head (BF) and medial hamstrings (MHs) during concentric and eccentric contractions at ±180 and ±60° s^?1. The knee flexors on the previously injured limb were weaker at all contraction speeds compared to the uninjured limb (+180° s^?1 p = 0.0036; +60° s^?1 p = 0.0013; ?60° s^?1 p = 0.0007; ?180° s^?1 p = 0.0007) whilst sEMG activity was only lower in the BF during eccentric contractions (?60° s^?1 p = 0.0025; ?180° s^?1 p = 0.0003). There were no between limb differences in MH sEMG activity or median power frequency from either BF or MH in the injured group. The uninjured group showed no between limb differences in any of the tested variables. Secondary analysis comparing the between limb difference in the injured and the uninjured groups, confirmed that previously injured hamstrings were mostly weaker (+180° s^?1 p = 0.2208; +60° s^?1 p = 0.0379; ?60° ^?1 p = 0.0312; ?180° s^?1 p = 0.0110) and that deficits in sEMG were confined to the BF during eccentric contractions (?60° s^?1 p = 0.0542; ?180° s^?1 p = 0.0473). Previously injured hamstrings were weaker and BF sEMG activity was lower than the contralateral uninjured hamstring. This has implications for hamstring strain injury prevention and rehabilitation which should consider altered neural function following hamstring strain injury.     

Metal ion dependence of DNA cleavage by SepMI and EhoI restriction endonucleases

Most of type II restriction endonucleases show an absolute requirement for divalent metal ions as cofactors for DNA cleavage. While Mg²⁺ is the natural cofactor other metal ions can substitute it and mediate the catalysis, however Ca²⁺ (alone) only supports DNA binding. To investigate the role of Mg²⁺ in DNA cleavage by restriction endonucleases, we have studied the Mg²⁺ and Mn²⁺ concentration dependence of DNA cleavage by SepMI and EhoI. Digestion reactions were carried out at different Mg²⁺ and Mn²⁺ concentrations at constant ionic strength. These enzymes showed different behavior regarding the ions requirement, SepMI reached near maximal level of activity between 10 and 20 mM while no activity was detected in the presence of Mn²⁺ and in the presence of Ca²⁺ cleavage activity was significantly decreased. However, EhoI was more highly active in the presence of Mn²⁺ than in the presence of Mg²⁺ and can be activated by Ca²⁺. Our results propose the two-metal ion mechanism for EhoI and the one-metal ion mechanism for SepMI restriction endonuclease. The analysis of the kinetic parameters under steady state conditions showed that SepMI had a K_m value for pTrcHisB DNA of 6.15 nM and a V_max of 1.79 × 10^?2 nM min^?1, while EhoI had a K_m for pUC19 plasmid of 8.66 nM and a V_max of 2 × 10^?2 nM min^?1.     

The effectiveness of stretch–shortening cycling in upper-limb extensor muscles during elite cross-country skiing with the double-poling technique

This investigation was designed to evaluate the effectiveness of stretch–shortening cycling (SSC_EFF) in upper-limb extensor muscles while cross-country skiing using the double-poling technique (DP). To this end, SSC_EFF was analyzed in relation to DP velocity and performance. Eleven elite cross-country skiers performed an incremental test to determine maximal DP velocity (V_max). Thereafter, cycle characteristics, elbow joint kinematics and poling forces were monitored on a treadmill while skiing at two sub-maximal and racing velocity (85% of V_max). The average EMG activities of the triceps brachii and latissimus dorsi muscles were determined during the flexion and extension sub-phases of the poling cycle (EMG_FLEX, EMG_EXT), as well as prior to pole plant (EMG_PRE). SSC_EFF was defined as the ratio of aEMG_FLEX to aEMG_EXT. EMG_PRE and EMG_FLEX increased with velocity for both muscles (P < 0.01), as did SSC_EFF (from 0.9 ± 0.3 to 1.3 ± 0.5 for the triceps brachii and from 0.9 ± 0.4 to 1.5 ± 0.5 for the latissimus dorsi) and poling force (from 253 ± 33 to 290 ± 36 N; P < 0.05). Furthermore, SSC_EFF was positively correlated to V_max, to EMG_PRE and EMG_FLEX (P < 0.05). The neuromuscular adaptations made at higher velocities, when more poling force must be applied to the ground, exert a major influence on the DP performance of elite cross-country skiers.     

Nitrate and phosphate uptake kinetics of the harmful diatom Eucampia zodiacus Ehrenberg,a causative organism in the bleaching of aquacultured Porphyra thalli

The diatom Eucampia zodiacus Ehrenberg is a harmful diatom which indirectly causes bleaching of aquacultured Nori (Porphyra thalli) through competitive utilization of nutrients during bloom events. In the present study, we experimentally investigated the nitrate (N) and phosphate (P) uptake kinetics of E. zodiacus, Harima-Nada strain. Maximum uptake rates (ρ_max), which were obtained by short-term experiments, were 0.777 and 0.916 pmol cell^?1 h^?1 for nitrate and 0.244 and 0.550 pmol cell^?1 h^?1 for phosphate at 9 and 20 °C, respectively. The half-saturation constants for uptake (K_s) were 2.59 and 2.92 μM N and 1.83 and 4.85 μM P at 9 and 20 °C, respectively. Although the maximum specific uptake rate (V_max; V_max = ρ_max/Q₀, Q₀; minimum cell quota) and V_max/K_s for nitrate at 9 °C are about 1/2 of those obtained at the optimum temperature (20 °C), they are still higher than those obtained for many other phytoplankton at their optimum temperature conditions for uptake. These results suggest that E. zodiacus utilizes nitrogen efficiently at low water temperature, and it is one of the important factors causing the serious damage to Porphyra thalli by bleaching due of this species. For phosphate, the K_s values of E. zodiacus were higher than those reported for other species; the V_max and V_max/K_s values were much lower than those of other diatoms such as Skeletonema costatum (Greville) Cleve. These results suggest that E. zodiacus is disadvantaged compared to other diatom species during competitive utilization of phosphate.     

Polyvinyl alcohol–silica nanohybrids: An efficient carrier matrix for amylase immobilization

Polyvinyl alcohol (PVA)–silica nanohybrids have been synthesized in a modified Stöber process. The bioactivities of the enzyme loaded hybrids were monitored and the optimum activity sample (H) was calcined at 300 °C in N₂ to obtain hybrid gel (H₃) with improved performance. The synthesized hybrids have been characterized by Fourier Transform Infra Red spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and BET surface area analysis. Under the optimized conditions, the bioactivity of the enzyme impregnated H₃ (H₃-Enz) was 21.823 U/mg. On recycling, H₃-Enz retained 88% of its initial bioactivity in the sixth cycle. The kinetic parameters of soluble starch hydrolysis for the immobilized (K_M = 4.137 mg mL^?1; V_max = 5.95 mg mL^?1 min^?1) and free enzyme (K_M = 10.667 mg mL^?1; V_max = 6.0557 mg mL^?1 min^?1) indicated that the immobilization has nearly doubled the enzyme's affinity for the substrate, while the maximum rate of the enzymatic reaction at the saturation point was not much affected. The immobilized enzyme showed greater shelf life in comparison to the free enzyme.     

Intramuscular fine-wire electromyography during cycling: Repeatability,normalisation and a comparison to surface electromyography

This study investigated (a) the feasibility and repeatability of intramuscular fine-wire electromyographic (fEMG) recordings from leg muscles during the repetitive, high-velocity cycling movement, (b) the influence of amplitude normalization technique on repeatability and statistical sensitivity, (c) the influence of test-retest interval duration on repeatability, and (d) differences between fEMG and surface EMG (sEMG) recordings of cycling. EMG activity of leg muscles was recorded using surface and fine-wire electrodes during one (n = 12, to investigate statistical sensitivity and compare sEMG and fEMG) or two sessions (T1 and T2, 5–20 days apart, n = 10, to investigate repeatability). fEMG recordings were feasible and there was high repeatability of fEMG recordings normalised to maximum measured EMG amplitude (MAX); mean coefficients of multiple correlation (CMC) ranged from .83 ± .13 to .88 ± .07. Data normalised to maximal (MVC) or submaximal contractions (sMVC) were less repeatable (p < .01). Statistical sensitivity was also greatest for data normalised to MAX (p < .01). Repeatability of fEMG increased with greater test-retest intervals (p < .01). The global pattern of muscle recruitment was consistent between sEMG and fEMG but sEMG recordings were characterized by additional myoelectric content. These findings support and guide the use of fEMG techniques to investigate leg muscle recruitment during cycling.     

Immobilization of apricot pectinesterase (Prunus armeniaca L.) on porous glass beads and its characterization

Pectinesterase isolated from Malatya apricot pulp was covalently immobilized onto glutaraldehyde-containing amino group functionalized porous glass beads surface by chemical immobilization at pH 8.0. The amount of covalently bound apricot PE was found 1.721 mg/g glass support. The properties of immobilized enzyme were investigated and compared to those of free enzyme. The effect of various parameters such as pH, temperature, activation energy, heat and storage stability on immobilized enzyme were investigated. Optimum pH and temperature were determined to be 8.0 and 50 °C, respectively. The immobilized PE exhibited better thermostability than the free one. Kinetic parameters of the immobilized enzyme (K_m and V_max values) were also evaluated. The K_m was 0.71 mM and the V_max was 0.64 μmol min^?1 mg^?1. No drastic change was observed in the K_m and V_max values. The patterns of heat stability indicated that the immobilization process tends to stabilize the enzyme. Thermal and storage stability experiments were also carried out. It was observed that the immobilized enzyme had longer storage stability and retained 50% of its initial activity during 30 days.     

Endurance and strength training effects on physiological and muscular parameters during prolonged cycling

PurposeThis study investigated the effects of a combined endurance and strength training on the physiological and neuromuscular parameters during a 2-h cycling test.MethodsFourteen triathletes were assigned to an endurance-strength training group and an endurance-only training group. They performed three experimental trials before and after training: an incremental cycling test to exhaustion, a maximal concentric lower-limbs strength measurement and a 2-h cycling exercise. Physiological parameters, free cycling chosen cadence and the EMG of Vastus Lateralis (VL) and Rectus Femoris (RF) were analysed during the 2-h cycling task before and after a strength training programme of 5 weeks (three times per week).ResultsThe results showed that the maximum strength and the isometric maximal voluntary contraction (isoMVC) after training were significantly higher (P < 0.01) and lower (P < 0.01) than those before training, respectively, in endurance-strength training group and endurance-only group. The physiological variables measured during the cycling tests and the progressive increase (P < 0.01) in EMGi_(VL) and EMGi_(RF) throughout the 2-h cycling test did not differ between the two groups before and after training, except for the variation of EMGi_(VL) over the cycle time which was stabilized during the second hour of the 2-h cycling test due to training in endurance-strength training group. The decrease in free cycling chosen cadence observed in pre-training (P < 0.01) was also replaced by a steady free cycling chosen cadence for the endurance-strength training group during the second hour of exercise.ConclusionThis study confirmed the decrease in the free cycling chosen cadence with exercise duration and demonstrated that a specific combined endurance and strength training can prevent this decrease during a 2-h constant cycling exercise.     

Extraction of hemoglobin with calixarenes and biocatalysis in organic media of the complex with pseudoactivity of peroxidase

The present work involves the use of p-tert-butylcalix[4,6,8]arene carboxylic acid derivatives (^tButyl[4,6,8]CH₂COOH) for selective extraction of hemoglobin. All three calixarenes extracted hemoglobin into the organic phase, exhibiting extraction parameters higher than 0.90. Evaluation of the solvent accessible positively charged amino acid side chains of hemoglobin (PDB entry 1XZ2) revealed that there are 8 arginine, 44 lysine and 30 histidine residues on the protein surface which may be involved in the interactions with the calixarene molecules. The hemoglobin–^tButyl[6]CH₂COOH complex had pseudoperoxidase activity which catalysed the oxidation of syringaldazine in the presence of hydrogen peroxide in organic medium containing chloroform. The effect of pH, protein and substrate concentrations on biocatalysis was investigated using the hemoglobin–^tButyl[6]CH₂COOH complex. This complex exhibited the highest specific activity of 9.92 × 10^?2 U mg protein^?1 at an initial pH of 7.5 in organic medium. Apparent kinetic parameters (V′_max, K′_m, k′_cat and k′_cat/K′_m) for the pseudoperoxidase activity were determined in organic media for different pH values from a Michaelis–Menten plot. Furthermore, the stability of the protein–calixarene complex was investigated for different initial pH values and half-life (t_1/2) values were obtained in the range of 1.96 and 2.64 days. Hemoglobin–calixarene complex present in organic medium was recovered in fresh aqueous solutions at alkaline pH, with a recovery of pseudoperoxidase activity of over 100%. These results strongly suggest that the use of calixarene derivatives is an alternative technique for protein extraction and solubilisation in organic media for biocatalysis.     

Metabolic,hygric and ventilatory physiology of the red-tailed phascogale (Phascogale calura; Marsupialia,Dasyuridae): Adaptations to aridity or arboreality?

The red-tailed phascogale is a small arboreal dasyurid marsupial that inhabits semi-arid to arid regions of Western Australia's wheat belt. Its body mass (34.7 g) is only ～15% of that predicted based on its phylogenetic position among other dasyuromorphs; we interpret this as an adaptation to its scansorial and semi-arid/arid lifestyle. The standard physiology of this species at a thermoneutral ambient temperature of 30 °C conforms to that of other dasyurid marsupials; body temperature (34.7 ± 0.37 °C), basal metabolic rate (0.83 ± 0.076 mL O₂ g^?1 h^?1), evaporative water loss (1.68 ± 0.218 mg H₂O g^?1 h^?1) and wet thermal conductance (3.8 ± 0.26 J g^?1 h^?1 °C^?1) all fall within the 95% predication limits for the respective allometric relationships for other dasyurid species. Thermolability confers an energy savings at low T_a and water savings at high T_a. Torpor, observed at low T_a, was found to be more beneficial for energy savings than for water economy. The red-tailed phascogale therefore has a physiology suitable for the challenges of arid environments without any obvious requirement for adaptations to its scansorial lifestyle, other than its considerably lower-than-expected body mass.     

Growth of the fungus Paecilomyces lilacinus with n-hexadecane in submerged and solid-state cultures and recovery of hydrophobin proteins

The filamentous fungus Paecilomyces lilacinus was grown on n-hexadecane in submerged (SmC) and solid-state (SSC) cultures. The maximum CO₂ production rate in SmC (V_max = 11.7 mg CO₂ L_g⁻¹ day⁻¹) was three times lower than in SSC (V_max = 40.4 mg CO₂ L_g⁻¹ day⁻¹). The P. lilacinus hydrophobin (PLHYD) yield from the SSC was 1.3 mg PLHYD g protein⁻¹, but in SmC, this protein was not detected. The PLHYD showed a critical micelle concentration of 0.45 mg mL⁻¹. In addition, the PLHYD modified the hydrophobicity of Teflon from 130.1 ± 2° to 47 ± 2°, forming porous structures with some filaments <1 μm and globular aggregates <0.25 μm diameter. The interfacial studies of this PLHYD could be the basis for the use of the protein to modify surfaces and to stabilize compounds in emulsions.     

Purification and characterization of an azoreductase from Escherichia coli CD-2 possessing quinone reductase activity

An oxygen-insensitive intracellular enzyme that is responsible for the decolorization of azo dyes was purified from Escherichia coli CD-2. The molecular weight of the purified enzyme was estimated as 27,000 ± 500 Da. Protein identification indicated that the enzyme had high sequence homology with E. coli K12 quinone reductase, and the enzyme was proved to have both azoreductase and quinone reductase activity. With methyl red as substrate, the optimal pH value and temperature were 6.5 and 37 °C, respectively. The enzyme was stable under different physiochemical conditions. The azoreductase activity was restrained by SDS and was almost completely inhibited by Co²⁺ and Hg²⁺. K_m and V_max values were 0.18 mM and 8.12 U mg^?1 of protein for NADH and 0.05 mM and 6.46 U mg^?1 of protein for methyl red, respectively. The purified enzyme could efficiently decolorize methyl red with both NADH and NADPH as electron donors.     

Enzymes that control the thiamine diphosphate pool in plant tissues. Properties of thiamine pyrophosphokinase and thiamine-(di)phosphate phosphatase purified from Zea mays seedlings

The pool of thiamine diphosphate (TDP), available for TDP-dependent enzymes involved in the major carbohydrate metabolic pathways, is controlled by two enzyme systems that act in the opposite directions. The thiamine pyrophosphokinase (TPK) activates thiamine into TDP and the numerous phosphatases perform the reverse two-step dephosphorylation of TDP to thiamine monophosphate (TMP) and then to free thiamine. Properties and a possible cooperation of those enzymes in higher plants have not been extensively studied. In this work, we characterize highly purified preparations of TPK and a TDP/TMP phosphatase isolated from 6-day Zea mays seedlings. TPK was the 29-kDa monomeric protein, with the optimal activity at pH 9.0, the K_m values of 12.4 μM and 4.7 mM for thiamine and ATP, respectively, and the V_max value of 360 pmol TDP min^?1 mg^?1 protein. The enzyme required magnesium ions, and the best phosphate donor was GTP. The purified phosphatase was the dimer of 24 kDa subunits, showed the optimal activity at pH 5.0 and had a rather broad substrate specificity, although TDP, but not TMP, was one of the preferable substrates. The K_m values for TDP and TMP were 36 μM and 49 μM, respectively, and the V_max value for TDP was significantly higher than for TMP (164 versus 60 nmoles min^?1 mg^?1 protein). The total activities of TPK and TDP phosphatases were similarly decreased when the seedlings were grown under the illumination, suggesting a coordinated regulation of both enzymes to stabilize the pool of the essential coenzyme.