Efficient estimation of temperature distribution, heat storage, thermocline migration and vertical eddy conductivities in stratified lakes

1. Factorial designs were used to investigate the spatial and temporal components of temperature sampling error in two medium-sized (maximum fetch = 9 and 11 km; maximum depth = 24 and 70m) Wisconsin lakes (Mendota and Green). Sampling designs were then optimized for estimating temperature distributions, thermocline migration, lake heat content, and vertical eddy conductivities in these and similar stratified lakes. 2. Errors were at a minimum for: (i) isotherms positioned ¹/₃ - ¹/₂ of the way down through the seasonal thermocline; (ii) at lake stations located near the node of the principal internal seiche; (iii) after an extended interval of low windpower. If seven spatially distributed lake stations were sampled n₁, n₂ times during the two low-power intervals bracketing a weather front, and the rime delay between revisits was randomized with respect to the period of the uninodal temperature seiches, the resulting standard error (cm) in ΔZ?₁₇ (depth of 17° isotherm; an unbiased, minimum-variance estimator for main thermocline migration) was (144/n₁+ 144/n₂)^1/2. If n₁=n₂= 2 ‘revisits’, the resulting CV (coefficient of variation) was 5–10% for ΔZ?₁₇ accompanying major individual cold fronts in early summer. 3. When estimating K_z, the vertical eddy conductivity, the most important component of error relates to ΔH_z, the change in heat content below depth z. The error in ΔH_z is minimized in the same manner as for lake-mean isotherm depth. Using the Mendota sampling design described above, the RMS error in ΔH_z decreases from ～90 cal cm^?2 in the upper metalimnion to ～35calcm^?2 near the base of the metalimnion. For seven take stations, and n₁= n₂= 2, K_z can be estimated with a CV ～10% bracketing a single major cold front. The CV decreases approximately as ΔH_z^?1, hence is roughly proportional to Δt^?1 or to (cumuiative windpower)^?1.     

A quantum mechanical study of the intrinsic helix-forming tendency of α-aminoisobutyric acid and dehydroalanine residues

A quantum mechanical study to compare the ability of α-aminoisobutyric acid (Aib), de-hydroalanine (ΔAla), and alanine (Ala) residues to stabilize helical conformations has been performed. To address the study, the oligopeptides X_n (X = Aib, ΔAla and Ala), where n varies from 1 to 6, were computed with the AM1 semiempirical method. The results show that the residues modified at the C^α carbon atom, Aib and ΔAla, are better helical formers than Ala. Thus, a cooperative energy effect was found for both residues, and especially for ΔAla. These terms permit the understanding the different conformational behaviors between Ala and its C^α-modified residues Aib and ΔAla. This trend is important for de novo protein design, where Aib and ΔAla must be considered useful residues in the design of synthetic helical motifs. © 1994 John Wiley & Sons, Inc.     

The stereodynamics of 1,2‐dipropyldiaziridines

N‐alkylated trans‐diaziridines are an intriguing class of compounds with two stereogenic nitrogen atoms which easily interconvert. In the course of our investigations of the nature of the interconversion process via nitrogen inversion or electrocyclic ring opening ring closure, we synthesized and characterized the three constitutionally isomeric diaziridines 1,2‐di‐n‐propyldiaziridine 1 , 1‐isopropyl‐2‐n‐propyldiaziridine 2 , and 1,2‐diisopropyldiaziridine 3 to study the influence of the substituents on the interconversion barriers. Enantiomer separation was achieved by enantioselective gas chromatography on the chiral stationary phase Chirasil‐β‐Dex with high separation factors α (1‐isopropyl‐2‐n‐propyldiaziridine: 1.18; 1, 2‐diisopropyldiaziridine: 1.24; 100°C 50 kPa He) for the isopropyl substituted diaziridines. These compounds showed pronounced plateau formation between 100 and 150°C, and peak coalescence at elevated temperatures. The enantiomerization barriers ΔG? and activation parameters ΔH? and ΔS? were determined by enantioselective dynamic gas chromatography (DGC) and direct evaluation of the elution profiles using the unified equation implemented in the software DCXplorer. Interestingly, 1‐isopropyl‐2‐n‐propyldiaziridine and 1,2‐diisopropyldiaziridine exhibit similar high interconversion barriers ΔG? (100°C) of 128.3 ± 0.4 kJ mol^?1 and 129.8 ± 0.4 kJ mol^?1, respectively, which indicates that two sterically demanding substituents do not substantially increase the barrier as expected for a distinct nitrogen inversion process. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

A calorimetric study of the binding of 2'-deoxyuridine-5'-phosphate and 5-fluoro-2'-deoxyuridine-5'-phosphate to thymidylate synthetase.

The thermodynamic parameters, ΔH′, ΔG′, and ΔS′, and the stoichiometry for the binding of the substrate 2′-deoxyuridine-5′-phosphate (dUMP) and the inhibitor 5-fluoro-2′-deoxyuridine-5′-phosphate (FdUMP) to Lactobacillus casei thymidylate synthetase (TSase) have been investigated using both direct calorimetric methods and gel filtration methods. The data obtained show that two ligand binding sites are available but that the binding of the second mole of dUMP is extremely weak. Binding of the first mole of dUMP can best be illustrated by dUMP + TSase + H⁺?(dUMP-TSase-H⁺). [1] The enthalpy, ΔH₁′, for reaction [1] was measured directly on a flow modification of a Beckman Model 190B microcalorimeter. Experiments in two different buffers (I = 0.10 m) show that ΔH₁′ = ?28 kJ mol^?1 and that 0.87 mol of protons enters into the reaction. Analysis of thermal titrations for reaction [1] indicates a free energy change of ΔG₁′ = ?30 kJ mol^?1 (K₁ = 1.7 × 10⁵ m^?1). From these parameters, ΔS₁′ was calculated to be +5 J mol^?1 degree^?1, showing that the reaction is almost totally driven by enthalpy changes. Gel filtration experiments show that at very high substrate concentrations, binding to a second site can be observed. Gel filtration experiments performed at low ionic strength (I = 0.05 m) reveal a stronger binding, with ΔG₁′ = ?35 kJ mol^?1 (K₁ = 1.2 × 10⁶ m^?1), suggesting that the forces driving the interaction are, in part, electrostatic. Addition of 2-mercaptoethanol (0.10 m) had the effect of slightly increasing the dUMP binding constant. Binding of FdUMP to TSase is best illustrated by 2FdUMP + TSase + n_HH⁺?FdUMP₂ ? TSase ? (H⁺)_nH. [2] The enthalpy for this reaction, ΔH₂, was also measured calorimetrically and found to be ?30 kJ mol^?1 with n_H = 1.24 at pH 7.4 Assuming two FdUMP binding sites per dimer as established by Galivan et al. [Biochemistry15, 356–362 (1976)] our calorimetric results indicate different binding energies for each site. Based on the binding data, a thermodynamic model is presented which serves to rationalize much of the confusing physical and chemical data characterizing thymidylate synthetase.     

Δ53β hydroxysteroid dehydrogenase activity of the rat corpus luteum exhibits positive substrate-binding co-operativity: A continuous monitoring microdensitometric study with unfixed ovarian tissue sections

Δ⁵3β hydroxysteroid dehydrogenase activity transforms biologically inactive Δ⁵3β hydroxy steroids into the active Δ⁴3-keto products (e.g. pregnenolone to progesterone). Using a cytochemical procedure which allows for the continuous microdensitometric monitoring of an enzyme reaction as it proceeds and a well described cytochemical assay for Δ⁵3β HSD we have analysed the initial velocity rates (V_o) for dehydroepiandrosterone (DHEA) binding to this enzyme in regressing (i.e. 20α hydroxy steroid dehydrogenase positive) corpus luteum (CL) cells in unfixed tissue sections (5 μm) of the dioestrous and proestrous rat ovary. The results are mean ± S.E.M. The relationship between DHEA concentration (0 to 50 μM) and Δ⁵3β HSD activity in the dioestrous corpora lutea was sigmoidal and had an atypical 1/V_o versus 1/S plot, the x intercept being positive. Using a 1/V_o versus 1/S² plot the V_max was determined to be 1·0 ± 0·08 μmol min^?1 mg^?1 CL (n = 6). The Hill constant was 2·7 ± 0·02 (n = 6) suggesting a high degree of positive co-operativity for DHEA binding. The S concentration for half maximal activity was 17 ± 1 μmoles (n = 6). In the corpora lutea cells of the proestrous ovary, the V_max for DHEA transformation was unchanged (0·95 ± 0·04 μmol min^?1 mg^?1, n = 3) whilst the S_0·5 was significantly increased to 27 ± 0·1 (p < 0·01, n = 3). The Hill constant remained positive being 2·9 ± 0·2 (n = 3). NAD⁺ binding to 3β HSD in regressing corpora lutea of the proestrous ovary has been demonstrated previously to be hyperbolic and fit the classical Michaelis-Menten model.¹ Extending the analysis of NAD⁺ binding to the regressing corpus luteum of the dioestrous rat ovary revealed similar kinetic characteristics to that seen with the proestrous enzyme, the apparent V_max and K_m being 0·84 ± 0·04 μmol min^?1 mg^?1 CL (n = 3) and 27 ± 7 μmol 1^?1 (n = 3) respectively. The Hill constant was 1·1 ± 0·03 (n = 3), indicating no co-operativity of co-factor binding.     

Synthesis and conformational study of peptides possessing helically arranged ΔZPhe side chains

Z-Dehydrophenylalanine (Δ^zPhe) possessing four oligopeptides, Boc-(L -Ala-Δ^zPhe-Aib)_n-OCH₃ (n = 1–4: Boc, t-butoxycarbonyl; Aib, α-aminoisobutyric acid), were synthesized, and their solution conformations were investigated by ¹H-nmr, ir, uv, and CD spectroscopy and theoretical CD calculation. ¹H-nmr (the solvent accessibility of NH groups) and ir studies indicated that all the NH groups except for those belonging to the N-terminal L -Ala-Δ^zPhe moiety participate in intramolecular hydrogen bonding in chloroform. This suggests that the peptides n = 2–4 have a 4 → 1 hydrogen-bonding pattern characteristic of 3₁₀-helical structures. The uv spectra of all these peptides recorded in chloroform and in trimethyl phosphate showed an intense maximum around 276 nm assigned to the Δ^zPhe chromophores. The corresponding CD spectra of the peptides n = 2–4 showed exciton couplets with a negative peak at longer wavelengths, whereas that of the peptide n = 1 showed only weak signals. Theoretical CD spectra were calculated for the peptides n = 2–4 of several helical conformations, on the basis of exciton chirality method. This calculation indicated that the three peptides form a helical conformation deviating from the perfect 3₁₀-helix that contains three residues per turn, and that their side chains of Δ^z Phe residues are arranged regularly along the helix. The center-to-center distance between the nearest phenyl pair(s) was estimated to be ～ 5.5 Å. The chemical shifts of the Δ^zPhe side-chain protons (H^β and aromatic H) for the peptides n = 2–4 indicated anisotropic shielding effect of neighboring phenyl group(s); the effect also supports a regular arrangement of the Δ^z Phe side chains along the helical axis. © 1993 John Wiley & Sons, Inc.     

A skew in poo: Biases in primate fecal isotope analysis and recommendations for standardized sample preparation

Feces are a treasure trove in the study of animal behavior and ecology. Stable carbon and nitrogen isotope analysis allows to assess the dietary niches of elusive primate species and primate breastfeeding behavior. However, some fecal isotope data may unwillingly be biased toward the isotope ratios of undigested plant matter, requiring more consistent sample preparation protocols. We assess the impact of this potential data skew in 114 fecal samples of wild bonobos (Pan paniscus) by measuring the isotope differences (Δ¹³C, Δ¹⁵N) between bulk fecal samples containing larger particles (>1 mm) and filtered samples containing only small particles (<1 mm). We assess the influence of fecal carbon and nitrogen content (ΔC:N) and sample donor age (subadult, adult) on the resulting Δ¹³C, Δ¹⁵N values (n = 228). Additionally, we measure the isotope ratios in three systematically sieved fecal samples of chimpanzees (Pan troglodytes verus), with particle sizes ranging from 20 μm to 8 mm (n = 30). We found differences in fecal carbon and nitrogen content, with the smaller fecal fraction containing more nitrogen on average. While the Δ¹³C values were small and not affected by age or ΔC:N, the Δ¹⁵N values were significantly influenced by fecal ΔC:N, possibly resulting from the differing proportions of undigested plant macroparticles. Significant relationships between carbon stable isotope ratios (δ¹³C) values and %C in large fecal fractions of both age groups corroborated this assessment. Δ¹⁵N values were significantly larger in adults than subadults, which should be of concern in isotope studies comparing adult females with infants to assess breastfeeding. We found a random variation of up to 3.0‰ in δ¹³C and 2.0‰ in nitrogen stable isotope ratios within the chimpanzee fecal samples separated by particle sizes. We show that particle size influences isotope ratios and propose a simple, cost-effective filtration method for primate feces to exclude larger undigested food particles from the analysis, which can easily be adopted by labs worldwide.     

Triple helix–coil transition of covalently bridged collagenlike peptides

The thermal triple helix–coil transition of covalently bridged collagenlike peptides with repeating sequences of (Ala-Gly-Pro)_n, n = 5–15, was studied optically. The peptides were soluble in water/acetic acid (99:1) and were found to form triple-helical structures in this solvent system beginning with n = 8. The thermodynamic analysis of the transition equilibrium curves for n = 9–13 yielded the parameters ΔH°_s = ?7.0 kJ per tripeptide unit, ΔS°_s = ?23.1 J deg^?1 mol^?1 per tripeptide unit for the coil-to-helix transition, and the apparent nucleation parameter σ ? 5 × 10^?2. It was suggested through double-jump temperature experiments that the rate-limiting step during refolding is not only influenced by the difficulties of nucleation, but also by cis–trans isomerization of the Gly-Pro peptide bond.     

The thermodynamics of the complexation of lanthanides by 1-hydroxy-4,7-disulfo-2-naphthoic acid

The thermodynamic parameters, log β, ΔH and ΔS, for formation of lanthanide-1-hydroxy-4,7- disulfo-2-naphthoic acid complexes have been determined at 25 °C in 0.10 M NaClO₄ solutions by potentiometric and calorimetric titrations. Under the experimental conditions, the data can be explained with the formation of LnL⁻, LnL₂⁵⁻ and LnHL complexes (H₂L²⁻ = 1-hydroxy-4,7-disulfo-2- naphthoic acid anion). At pH < 3 the LnHL complex is the major species, whereas by increasing pH the formation of LnL_n³⁻⁴ⁿ complexes becomes more important. The data are compared to the comparable data for complexing by aromatic carboxylic acids.     

Detecting trophic‐level variation in consumer assemblages

1. Stable isotopes of nitrogen are useful for quantifying the trophic structure of food webs, but only if the variation in trophic enrichment (Δ_N), which is the difference in δ¹⁵N between a consumer and its food, is small relative to the value of Δ_N itself. 2. We examined the sources of variation in zooplankton Δ_N by measuring the trophic enrichment (Δ_N) of seven species of freshwater cladocerans, and by testing for an effect of age and temperature on the Δ_N of Daphnia pulicaria. 3. We found that Δ_N was similar among Cladocera and was not correlated with body size. Overall, the Δ_N for D. pulicaria was 1.4‰ (SE = 0.69, n = 57), as was expected for the detritus diet that we used in our experiments. We found no effect of temperature (15–25 °C) on Δ_N, but found that Δ_N of D. pulicaria increased with increasing age (10–30 days). 4. We developed a new method to test for trophic‐level variation in a group of consumers that explicitly accounts for the uncertainty in Δ_N. Using this approach, we confirmed that natural assemblages of zooplankton feed at several trophic levels in lake food webs.     

Sterols and fatty acids of the marine diatom biddulphia sinensis

Nine sterols, most showing Δ⁵- or Δ^5,22-unsaturation, were identified in the marine diatom Biddulphia sinensis. One sterol, cholesta-5,22E-dien-3β-ol, comprised 70–80% of the total sterols which is the first such predominance noted in a diatom. The only Δ⁷-sterol detected was cholest-7-en-3β-ol and this was a very minor component. A sterol showing unusual side-chain alkylation,23,24-dimethylcholesta-5,22E-dien-3β-ol, was identified for the first time in a diatom. Total fatty acids exhibited a predominance of Δ⁹- 16:1, 14:0, 20:5 and 16:0, typical of diatoms, although the proportions of these acids were found to vary with culture maturity. n-Heneicosahexaene was the major hydrocarbon together with a small amount of squalene.     

Inhibitory effects of alkyl gallate and its derivatives on fatty acid desaturation

Alkyl gallate, which is known as an antioxidant, intensively inhibited Δ5 and Δ6 desaturation in both rat liver microsomes and an arachidonic acid-producing fungus Mortierella alpina 1S-4. The rat liver microsomal Δ5 and Δ6 desaturases were inhibited by gallic acid esterified with alcohols with various numbers of carbons, suggesting that the necessary structure in an esterified alcohol for the inhibition is not so strict. Among the three hydroxy groups in gallic acid, the m-hydroxy group was shown to be the necessary structure. Kinetic analyses revealed that propyl gallate is a noncompetitive inhibitor of Δ5 desaturase (K_i = 2.6 · 10⁻⁵ M) and Δ6 desaturase (K_i = 1.7 · 10⁻⁴ M). These data indicate that alkyl gallate is a new type of desaturase inhibitor and different from known natural inhibitors, i.e., sesamin and curcumin.     

Co-occurrence of Δ5- and Δ7 -sterols in the fungus Dictyuchus monosporus

The desmethyl sterol composition of the oomycete Dictyuchus monosporus is unusual in that it is a mixture of 56.9 % Δ⁵-sterols and 42.6 % Δ⁷-sterols. The Δ⁵-sterols are cholesterol, 24 methylenecholesterol and fucosterol; the Δ⁷-sterols are cholest-7-enol, ergosta-7,24(28)-dienol and stigmasta-7,E-24(28)-dienol. Stigmasta-7,E-24(28)-dienol, is identified for the first time from natural sources. In addition, traces of lanosterol are present.     

What is the invasiveness of <Emphasis Type="Italic">Hemimysis anomala</Emphasis> (Crustacea,Mysidae) in the large deep Lake Bourget,France?

Application of stable isotope data to trophic studies requires understanding of factors influencing the isotopic discrimination factor (Δ) between consumers and their prey resources. This is missing for many omnivorous species, despite their diet and environment potentially impacting Δ. The effects of temperature, diet (including formulated feeds) and tissue type on Δ¹³C and Δ¹⁵N were thus tested experimentally. A temperature experiment exposed three species to identical diets at 18 and 23°C, whereas a diet experiment exposed one species to four diets at 18°C. At 23°C, C:N ratios, Δ¹³C and Δ¹⁵N were generally elevated versus 18°C. After lipid correction, tissue/species-specific differences at 23°C in Δ¹³C and Δ¹⁵N were up to 0.73 and 0.54‰ higher, respectively. Across the four diets, there were also significant differences in Δ¹³C and Δ¹⁵N between a natural diet and diets based on formulated feeds. Δ¹³C and Δ¹⁵N of muscle were 1.51 to 2.76‰ and 3.13 to 5.44‰, respectively. Highest Δ for both isotopes was from a formulated feed based on plant material that resulted in lower dietary protein content and quality. Thus, diet and environment fundamentally affected the isotopic discrimination factors and these factors require consideration within trophic studies based on stable isotopes.     

An Arabidopsis mutant deficient in sterol biosynthesis: heterologous complementation by ERG 3 encoding a Δ7-sterol-C-5-desaturase from yeast

The mutant STE 1 was isolated by screening an ethylmethane sulfonate (EMS)-mutagenized population of Arabidopsis thaliana which consisted of 22 000 M₂ plants divided into 1100 pools of 20 plants by gas chromatography of sterols extracted from small leaf samples. STE 1 was characterized by the accumulation of three Δ⁷-sterols concomitantly with the decrease of the three corresponding Δ⁵-sterols which are the end products of the sterol pathway in wild-type leaves. The structure of these Δ⁷-sterols was determined after two steps of purification on HPLC, by gas chromatography coupled with mass spectrometry (GC-MS) and proton nuclear magnetic resonance spectrometry (¹H-NMR). The accumulation of Δ⁷-sterols suggested that the mutant is deficient in the activity of the Δ⁷-sterol-C-5-desaturase. Genetic analysis showed that the accumulation of Δ⁷-sterols was due to a single recessive nuclear mutation. The mutant line STE 1 was backcrossed four times to the wild-type. The resulting STE 1 plants had wild-type morphology and set seeds normally, suggesting that the Δ⁷-sterols in STE 1 are good surrogates of physiologically active Δ⁵-sterols to sustain normal development. STE 1 roots were transformed with the Saccharomyces cerevisiae ERG 3 gene encoding the Δ⁷-sterol-C-5-desaturase under the control of the CaMV 35S promoter. Seven transgenic STE 1 root-derived calli showed an increase in Δ⁵-sterols and a concomitant decrease in Δ⁷-sterols in comparison with STE 1 untransformed root-derived calli. Northern blot analysis using the ERG 3 probe showed a strong expression of ERG 3 in three of the seven transgenic calli. These results suggest that the accumulation of Δ⁷-sterols in the STE 1 mutant is due to a deficiency of the Δ⁷-sterol-C-5-desaturation step in the plant sterol biosynthesis pathway.     

Effects of body size and environment on diet-tissue δN fractionation in fishes

Nitrogen stable isotope natural abundance data are often used in trophodynamic research. The assumed nitrogen diet-tissue fractionation (Δδ¹⁵N) determines conclusions about trophic level, potential food sources and ontogenetic diet shifts. Δδ¹⁵N is usually assumed to be 3.0-3.4‰ per trophic level and unaffected by the size or age of animals or their environment. To assess the effects of body size, experimental duration and environmental conditions on fish tissue Δδ¹⁵N, two populations of European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) muscle or sandeel (Ammodytes marinus) for 2 years under natural light and temperature regimes. Bass were sampled at approximately monthly intervals to determine Δδ¹⁵N for muscle, heart and liver tissue. Mean values of Δδ¹⁵N were 3.83‰, 3.54‰, 2.05‰ (sandeel diet) and 3.98‰, 3.32‰, 1.95‰ (dab diet) for muscle, heart and liver tissue respectively. The assumption that fractionation was independent of body mass was upheld for muscle and heart tissue, but not for liver. Time effects on muscle Δδ¹⁵N were explainable by a sinusoidal function with a period of 1 year and wave height ∼ 0.3‰. Time resulted in increases in heart δ¹⁵N and decreases in liver δ¹⁵N which were small compared to background variation, equating to 1/6 of a trophic level over 2 years, and unlikely to have great significance in ecological studies. Heart and liver δ¹⁵N were also affected by temperature probably reflecting the metabolic functions of these tissues and their associated rates of turnover. However in heart the explanatory power of temperature appeared tied to that of time. Although the Δδ¹⁵N for bass muscle on both diets approached 4‰, the Δδ¹⁵N values from this study, when combined with those from the literature, suggest that where fish species specific data are not available, a mean Δδ¹⁵N for fish muscle of 3.2‰ should be applied (mean white muscle Δδ¹⁵N = 3.15). The literature based mean Δδ¹⁵N for whole fish was lower than that of white muscle suggesting that a separate Δδ¹⁵N (2.9‰) should be applied when sampling whole fish.     

Unfolding thermodynamics of the Delta-domain in the prohead I subunit of phage HK97: determination by factor analysis of Raman spectra

An early step in the morphogenesis of the double-stranded DNA (dsDNA) bacteriophage HK97 is the assembly of a precursor shell (prohead I) from 420 copies of a 384-residue subunit (gp5). Although formation of prohead I requires direct participation of gp5 residues 2-103 (Δ-domain), this domain is eliminated by viral protease prior to subsequent shell maturation and DNA packaging. The prohead I Δ-domain is thought to resemble a phage scaffolding protein, by virtue of its highly α-helical secondary structure and a tertiary fold that projects inward from the interior surface of the shell. Here, we employ factor analysis of temperature-dependent Raman spectra to characterize the thermostability of the Δ-domain secondary structure and to quantify the thermodynamic parameters of Δ-domain unfolding. The results are compared for the Δ-domain within the prohead I architecture (in situ) and for a recombinantly expressed 111-residue peptide (in vitro). We find that the α-helicity (∼ 70%), median melting temperature (T_m = 58 °C), enthalpy (ΔH_m = 50 ± 5 kcal mol^− 1), entropy (ΔS_m = 150 ± 10 cal mol^− 1 K^− 1), and average cooperative melting unit (〈n_c〉 ∼ 3.5) of the in situ Δ-domain are altered in vitro, indicating specific interdomain interactions within prohead I. Thus, the in vitro Δ-domain, despite an enhanced helical secondary structure (∼ 90% α-helix), exhibits diminished thermostability (T_m = 40 °C; ΔH_m = 27 ± 2 kcal mol^− 1; ΔS_m = 86 ± 6 cal mol^− 1 K^− 1) and noncooperative unfolding (〈n_c〉 ∼ 1) vis-à-vis the in situ Δ-domain. Temperature-dependent Raman markers of subunit side chains, particularly those of Phe and Trp residues, also confirm different local interactions for the in situ and in vitro Δ-domains. The present results clarify the key role of the gp5 Δ-domain in prohead I architecture by providing direct evidence of domain structure stabilization and interdomain interactions within the assembled shell.     

Effects of body size and environment on diet-tissue δC fractionation in fishes

δ¹³C data are often used in trophodynamic research where diet-tissue fractionation (Δδ¹³C) is assumed to be 0-1‰ per trophic level and unaffected by the size of animals or their environment. Variation in Δδ¹³C will influence conclusions about food sources, energy pathways and trophic level. To assess the effects of body size, age and environmental conditions on Δδ¹³C, European sea bass (Dicentrarchus labrax) were reared on constant diets of dab (Limanda limanda) or (Ammodytes marinus) for 2years under natural environmental regimes. Bass were sampled approximately monthly to determine Δδ¹³C for muscle, heart and liver tissue and were 1.66‰, − 0.18‰, − 1.77‰ (sandeel diet) and 1.34‰, − 1.18‰, − 1.75‰ (dab diet) respectively. Arithmetic lipid correction increased Δδ¹³C to > 2‰ for muscle and liver. Δδ¹³C was dependent on body mass and experimental duration (age) and generally declined with weight or time even after correction for lipid content. For liver, increasing temperature increased Δδ¹³C. The Δδ¹³C estimates from this study were compared with all available published Δδ¹³C estimates for fish. Bass muscle Δδ¹³C was similar to previous estimates for fish white muscle Δδ¹³C (1.56 ± 1.10‰) and whole body Δδ¹³C (1.52 ± 1.13‰). Fractionations derived in this study, combined with those from the literature, support the use of diet-tissue fractionation values of between 1‰-2‰ for δ¹³C, rather than the commonly used 0‰ − 1‰. For muscle Δδ¹³C, 1.5‰ is appropriate.     

Microcalorimetry of microorganism metabolism of monosaccharides and simple aromatic compounds

Heat conduction solution enable rapid determination of the heats of aerobic and anaerobic metabolism of substrate by microorganisms. Aliquots of 1.0 ml cell suspension, 5 × 10⁹ cell/ml, were mixed with a few dozen nmol substrate contained in 0.5 ml, under a controlled atmosphere of air, O₂, or N₂. At these substrate concentration, with adapted microorganisms, metabolism and its heat generation are usually complete within 300 to 600 sec. The raw data yield ΔH_app values. The ΔH_app were determined in the range 0.001 to 0.010% substrate, and extrapolated (limit substrate concentration →0), to yield Δ⁰H?, the limiting differential molar heat of metabolism. The Δ⁰H? values express the heat generated when there is rapid metabolism but little new growth, minimal contribution by H⁺ transfer from metabolites, and maintenance of aerobicity or anaerobicity as specified. Escherichiacoli B/5 was used for aerobic and anaerobic combustion of eight sugars. Pseudomonas multivorans, and an Acinetobacter, strain B-1, were used for aerobic metabolism of benzene, toluene, naphthalene, and a methylnaphthalene. The larger heats of combustion of the hydrocarbons enable the use of aqueous solutions of hydrocarbons well below their solubility limits. The quotient Δ⁰H?/n (n = atoms carbon/molecule substrate) varies from (-)36 to (-)67 kcal/mol carbon for the sugars. The most reduced sugar yields the largest exothermic heats. The quotient varies from (-)27 to (-)81 kcal/mol carbon for the aromatic hydrocarbons. Comparison of the calorimetric heats of metabolism of those from total aerobic combustion in aquo (where available) give measure of the efficiencies with which the heat contents of the aqueous substrate are used by the bacteria.     

Probing into the binding interaction between medroxyprogesterone acetate and bovine serum albumin (BSA): spectroscopic and molecular docking methods

To further understand the mechanism of action and pharmacokinetics of medroxyprogesterone acetate (MPA), the binding interaction of MPA with bovine serum albumin (BSA) under simulated physiological conditions (pH 7.4) was studied using fluorescence emission spectroscopy, synchronous fluorescence spectroscopy, circular dichroism and molecular docking methods. The experimental results reveal that the fluorescence of BSA quenches due to the formation of MPA–BSA complex. The number of binding sites (n) and the binding constant for MPA–BSA complex are ~1 and 4.6 × 10³ M^?1 at 310 K, respectively. However, it can be concluded that the binding process of MPA with BSA is spontaneous and the main interaction forces between MPA and BSA are van der Waals force and hydrogen bonding interaction due to the negative values of ΔG⁰, ΔH⁰ and ΔS⁰ in the binding process of MPA with BSA. MPA prefers binding on the hydrophobic cavity in subdomain IIIA (site II′′) of BSA resulting in a slight change in the conformation of BSA, but BSA retaining the α‐helix structure. Copyright © 2016 John Wiley & Sons, Ltd.