Heat capacity changes and partial molal heat capacities of some di- and tripeptides in water

Integral enthalpies of solution of several dipeptides and tripeptides in water at low concentrations have been determined at 25 and 35°C. These data have been used to derive the changes in heat capacity on dissolution at infinite dilution ΔC at 30°C. Limiting partial molal heat capacities ΔC have been determined by combining ΔC with C_p2 (heat capacity of pure solid peptides). Using the data on ω-amino acids and these peptides, the partial molal heat capacity of a peptide group ? CONH? was semiquantitatively estimated.     

Effect of calcium chloride on the conformation of proteins. Thermodynamic studies of some model compounds

Partial molar heat capacities (CP2 degrees) and volumes (V2 degrees) for some amino acids and peptides were measured in 1 M aqueous calcium chloride solutions at 298.15 degrees K using a Picker flow microcalorimeter and an oscillating-tube digital density meter. Using the data for these amino acids and peptides in water, the corresponding partial molar heat capacities of transfer (CP2,tr degree) and volumes (V2,tr degree) from water to 1 M aqueous calcium chloride were deduced. These thermodynamic parameters are significantly positive, indicating that strong interactions occur between the ions of calcium chloride and the charged centres of these amino acids and peptides. A comparison has been made with a similar transfer of these compounds to sodium chloride solutions. The thermodynamic parameters of the transfer of peptide group (-CONH) are much more positive in calcium chloride than in sodium chloride solutions. The implication of this result for the ability of calcium chloride to act as a stronger destabilizer of protein conformation is discussed.     

Apparent molar volumes of some amino acids and peptides in aqueous urea solutions

Densities of solutions of several α-amino acids and peptides in 3 and 6m aqueous urea solvents have been determined at 298.15 K. These data have been used to evaluate the infinite-dilution apparent molar volumes of the solutes and the volume changes due to transfer (V ) of the α-amino acids and peptides at infinite dilution from water to aqueous urea solutions. The sign and magnitude of the V values have been rationalized in the framework of Friedman's cosphere-overlap model. The V values for the glycyl group (? CH₂CONH? ) and alkyl side chains have been estimated.     

Heat capacities of protein functional groups

Using a precise technique of scanning calorimetry the heat capacities of a series of carboxylic acids and their sodium salts, alcohols, and N-substituted amides have been measured from 5 to 100 degrees C. From these data, the partial molar heat capacities of CH2, CONH, COOH, and COONa groups have been determined. It is shown that the heat capacity of the CH(2) group in aqueous solution is independent of the type of compound used for its determination, is positive at low temperature, and is linearly decreasing in magnitude with an increase in temperature. In contrast, the heat capacities of COOH and COONa groups in aqueous solution are negative at room temperature and their magnitude non-linearly decreases with an increase in temperature. It appears that the partial heat capacity of CONH group in aqueous solution depends on the type of model compound used for its determination. These differences correlate with the difference in the water accessible surface area of atoms in the CONH group in different model compounds.     

Solubilities of amino acids

The Mettler/Paar precision density meter DMA-02D has been used to determine the concentration of saturated solutions of amino acids at 20.0, 25.0, and 29.8 °C. The technique has proven itself an elegant and precise method. The solubilities of all of the amino acids with the exceptions of proline, lysine, and cystine have been measured. The Gibbs free energies of transfer from saturated water solution to 1M Na₂SO₄ and to 1M Gu·HCL along with the van't Hoff heats and entropies have been calculated. The van't Hoff heats have been compared with the calorimetrically determined heats for some of the amino acids. The Lumry-Rajender relation between the entropy and heats has been observed. The process of transfer of the amino acids from water to the solvents is primarily enthalpic rather than entropic.     

Assessment of hemolytic activity of bee venom against some physicochemical factors

Bee venom (BV) is a biotoxin with biologically active peptides which have cell lysis and hemolytic activity properties. These properties can be affected under different storage conditions or during the production process. In present study, we investigated effects of a number of physicochemical factors, including temperature, pH, UV radiation, ultrasound waves and storage time on hemolytic activity of BV. Maximum absorption and melting temperature of BV solution were obtained as 280 nm and ~70 °C, respectively. Cell hemolysis 50 (CH₅₀) -concentration of BV that can lyse 50% of red blood cells- was determined as 0.94 μg/ml at ambient temperature. CH₅₀ was shown not to be importantly varied at temperature up to 60 °C, pH value 2 to 13 and under UV/ ultrasound radiation. Storage at ?20, 6 and 25 °C for 6 months made about 2.5, 35 and 1000 times increase in CH₅₀. From the results, it may be concluded that BV is a relatively resistant hemolytic agent and can be used in a variety of laboratory research and product manufacturing methods.     

An Evaluation of the Critical Parameters for Abiotic Peptide Synthesis in Submarine Hydrothermal Systems

It has been proposed that oligopeptides may be formed in submarine hydrothermal systems (SHSs). Oligopeptides have been synthesized previously under simulated SHS conditions which are likely geochemically implausible. We have herein investigated the oligomerization of glycine under SHS–like conditions with respect to the limitations imposed by starting amino acid concentration, heating time, and temperature. When 10⁻¹ M glycine solutions were heated at 250°C for < 20 min glycine oligomers up to tetramers and diketopiperazine (DKP) were detectable. At 200°C, less oligomerization was noted. Peptides beyond glycylglycine (gly₂) and DKP were not detected below 150°C. At 10⁻² M initial glycine concentration and below, only gly₂, DKP, and gly₃ were detected, and then only above 200°C at < 20 min reaction time. Gly₃ was undetectable at longer reaction times. The major parameters limiting peptide synthesis in SHSs appear to be concentration, time, and temperature. Given the expected low concentrations of amino acids, the long residence times and range of temperatures in SHSs, it is unlikely that SHS environments were robust sources of even simple peptides. Possible unexplored solutions to the problems presented here are also discussed.     

Operational temperature regulates anodic biofilm growth and the development of electrogenic activity

The operational temperature of microbial fuel cell reactors influences biofilm development, and this has an impact on anodic biocatalytic activity. In this study, we compared three microbial fuel cell (MFC) reactors acclimated at 10°C, 20°C and 35°C to investigate the effect on biomass development, methanogenesis and electrogenic activity over time. The start-up time was inversely influenced by temperature, but the amount of biomass accumulation increased with increased temperatures, the 10°C, 20°C and 35°C acclimated biofilms resulted in 0.57, 0.82 and 5.43 g biomass (volatile suspended solids) per litre respectively at 56 weeks of operation. Biofilm build-up on the 35°C anode was further demonstrated by scanning electron microscopy, which showed large aggregations of biomass accumulating on the anode when compared to 10°C and 20°C biofilms. Biomass accumulation had a direct impact on biocatalytic performance, with the maximum power at 35°C after 60 weeks of operation being 2.14 W m⁻³ and power densities for the 10°C and 20°C reactors being and 4.29 W m⁻³. Methanogenic activity was also shown to be higher at 35°C, with a rate of 10.1 mmol CH₄ biofilm per gram of volatile suspended solid (VSS) per day, compared to 0.28 mmol CH₄ per gram of VSS per day produced at 20°C. These results demonstrate that higher MFC operating temperatures could be detrimental to the biocatalytic performance of electrochemically active bacteria in anodic biofilms due to biomass accumulation with enhanced development of non-electrogenic communities (e.g. methanogens and fermenters), meaning that, over time, psychro- or mesophilic operation can have beneficial effects for the development of electrogenically active populations in the reactor.     

Effects of cavity-creating mutations on conformational stability and structure of the dimeric 4-α-helical protein ROP: Thermal unfolding studies

The structural and energetic perturbations caused by cavity-creating mutations (Leu-41 → Val and Leu-41 → Ala) in the dimeric 4-α-helical-bundle protein ROP have been characterized by CD spectroscopy and differential scanning calorimetry (DSC). Deconvolution of the CD spectra showed a decrease in α -helicity as a result of the amino acid exchanges that follows qualitatively the overall decrease in conformational stability. Transition enthalpies are sensitive probes of the energetic change associated with point mutations. ΔH⁰ values at the respective transition temperatures, T_1/2 (71.0, 65.3, and 52.9°C at 0.5 mg/ml) decrease from 580 ± 20 to 461 ± 20 kJ/(mol of dimmer) and 335 ± 20 kJ/(mol of dimmer) for wildtype ROP (Steif, C., Weber, P., Hinz, H.-J., Flossdorf, J., Cesareni, G., Kokkinidis, M. Biochemistry 32:3867-3876, 1993), L⁴¹V, and L⁴¹A, respectively. The conformational stabilities at 25°C expressed by the standard Gibbs energies of denaturation, ΔG, are 71.7, 61.1, and 46.1 kJ/(mol of dimmer). The corresponding transition enthalpies have been obtained from extrapolation using the c(T)and c(T) functions. Their values at 25°C are 176.3, 101.9, and 141.7 kJ/(mol of dimmer) for wild-type ROP, L⁴¹V, and L⁴¹A, respectively. When the stability perturbation resulting from the cavity creating mutations is referred to the exchange of 1 mol of CH₂ group, the average ΔΔG value is ?5.0 ± 1 kJ/(mol of CH₂ group). This decrease in conformation stability suggests that dimeric ROP exhibits the same susceptibility to Leu → Yal and Leu → Ala exchanges as small monomeric proteins. Careful determinations of the partial specific heat capacities of wild-type and mutated protein solutions suggest that the mutational effects are predominantly manifested in the native rather than the unfolded state. © 1995 Wiley-Liss, Inc.     

Arginine Metabolising Enzymes as Therapeutic Tools for Alzheimer’s Disease: Peptidyl Arginine Deiminase Catalyses Fibrillogenesis of β-amyloid Peptides

The accumulation of arginine in the cerebrospinal fluid and brains of patients suffering from acute neurodegenerative diseases like Alzheimer’s disease, point to defects in the metabolic pathways involving this amino acids. The deposits of neurofibrillary tangles and senile plaques perhaps as a consequence of fibrillogenesis of β-amyloid peptides has also been shown to be a hallmark in the aetiology of certain neurodegenerative diseases. Peptidylarginine deiminase (PAD II) is an enzyme that uses arginine as a substrate and we now show that PAD II not only binds with the peptides Aβ_1-40, Aβ_22-35, Aβ_17-28, Aβ_25-35 and Aβ_32-35 but assists in the proteolytic degradation of these peptides with the concomitant formation of insoluble fibrils. PAD was purified in 12.5% yield and 137 fold with a specific activity of 59 μmol min^?1?mg^?1 from bovine brain by chromatography on diethylaminoethyl (DEAE)-Sephacel. Characterisation of the enzyme gave a pH and temperature optima of 7.5°C and 68°C, respectively, and the enzyme lost 50% activity within 38 min at this temperature. Michaelis-Menten kinetics established a V _max and K _m of 1.57 μmol min^?1?ml^?1 and 1.35 mM, respectively, with N-benzoyl arginine ethyl ester as substrate. Kinetic analysis was used to measure the affinity (K _i) of the amyloid peptides to PAD with values between 1.4 and 4.6 μM. The formation of Aβ fibrils was rate limiting involving an initial lag time of about 24 h that was dependent on the concentration of the amyloid peptides. Turbidity measurements at 400 nm, Congo Red assay and Thioflavin-T staining fluorescence were used to establish the aggregation kinetics of PAD-induced fibril formation.     

NMR study of the structure of short-chain peptides in solution.

The electron-mediated spin–spin coupling constant J between the amide NH and the α-CH protons in the dipeptide fragment C^α? CO(NH? C^αH)R? C′ONH? C^α is dependent on the dihedral angle of rotation (Φ) around the N? C bond. Measurement of J in a series of zwitterionic dipeptides H₃N⁺? CHR₁? CONH? CHR₂? CO₂^? (which is conformationally similar to the dipeptide fragment) in TFA solution shows that J is independent of R₁, but dependent on the steric bulk of R₂. The data are interpreted in terms of a model that assumes that what we measure is an average value of J? a thermal average over all the possible rotamers. The groups R₁ and R₂ are, in most cases, sterically kept apart by the trans and planar amide bonds, and hence the independence of J of R₁. This model is consistent with the theoretical calculations done on the dipeptide fragment. The effect of the structural characteristics of the side chains (e.g., the effect of lengthening and branching the side chains) on the J values in dipeptides is discussed in the light of the existing results of theoretical calculations. Study of 〈J〉 values in tripeptides (C₆H₅CH₂OCONH? CHR₁? CONH? CHR₂? CO₂CH₃, essentially three linked peptide units) shows that electrostatic interaction between the two amide bonds modifies the potential energy surface and the 〈J〉 value of a dipeptide subunit in the tripeptides. Also in some cases, direct steric interaction between the two side chains in the two adjacent dipeptide subunits in the tripeptide affects the potential energy surfaces of the individual dipeptide subunits and hence the 〈J〉 values. The influence of the structural characteristics of the side chains of individual amino acids on structure formation at or beyond the dipeptide level is discussed at various points. The J(NH? ^αCH) values of CH₃CONH? CHR? CONH₂ and CH₃CONH? CHR? CO₂CH₃ with the same R are quite different for R = valine, leucine, phenylalanine, methionine, but equal for R = glycine. This, coupled with the fact that one of the carboxamide NH resonances has a chemical shift different from its counterpart in simple amides like CH₃CONH₂ and the other carboxamide NH has the same chemical shift as its counterpart in CH₃CONH₂, suggest the presence of a hydrogen bond in dipeptide CH₃CONH? CHR? CONH₂ with carboxamide NH as the donor. Theoretical evidence for two seven-membered hydrogen-bonded rings with the carboxamide NH as donor and the acetyl oxygen as acceptor is summarized. Our data cannot suggest the number of such hydrogen-bonded rings, nor can they conclude the relative proportion of these rings in a particular dipeptide. A discussion of the difficulty of interpretation is presented and the data are discussed under certain simplifying assumptions.     

Effects of urea and guanidine hydrochloride on peptide and nonpolar groups

The free energy transfer of several N-acetyl(glycine)n ethyl esters (n = 1-3) and side chain derivatives (Ala, Val, Nva, Leu, Nle, and Phe) from water to urea and guanidine hydrochloride solutions has been determined from the solubility and distribution coefficients of these compounds between aqueous and nonaqueous phases. These uncharged model peptides, unlike the amino acids used for a similar study, avoid complication due to charge effects for the transfer process. The compounds with an increase in the number of glycyl groups show additivity of the group free energy toward the transfer from water to urea solution but not to guanidine hydrochloride solution. The derivatives with a side chain show that the principle of group additivity does not hold true for the aliphatic side chains for the transfer to either urea or guanidine hydrochloride solutions. In fact, the free energy of transfer of the side chains, viz., aliphatic ones, is found to be energetically unfavorable in moderately high denaturant concentration. Phenylalanyl, the only aromatic side chain studied here, showed a favorable free energy of transfer to the denaturant solutions. In addition, the values of the favorable free energy obtained in this study are much smaller than the values obtained from the study of the amino acids. The transfer of the glycyl group to the denaturant solutions is exothermic whereas the transfer of the side chains is endothermic in nature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calorimetric studies of the interactions of guanidinium hydrochloride and potassium iodide with model amides in aqueous solution.

The enthalpies of transfer, ΔH_tr, of a series of amides from water to aqueous solutions of either guanidinium hydrochloride (GuHCl) or potassium iodide were obtained from calorimetric measurements at 25°C. The amides were studied at molalities around 10^?2 m while salt molalities ranged from 0–10 m. The amides investigated were Ac-Gly-NHMe, Ac-Gly-Gly-NHMe, Ac-Ala-NHMe, and Ac-Leu-NHMe. Use of an additivity assumption allowed the calculation of group contributions to ΔH_tr in these two salt systems for the methyl group, leucyl side chain, and the peptide backbone unit. Values of the entropy of transfer were also obtained. The great ability of GuHCl to randomize protein structures appears to arise from effects on polar and nonpolar groups, which are characterized by enthalpies and entropies of transfer not substantially different from those with KI, a salt comprised of ions of comparable size and polarizability. The difference in the sign of the free energies of transfer of nonpolar groups from water to MX solutions, negative for GuHCl and positive for KI, is the result of these small differences in enthalpies and entropies of transfer. Variations in water structure produced by differences in ionic properties rather than a mode of action for GuHCl very different from that of other salts characterizes its superior denaturing ability.     

26 Inversion approach to the origin of life: theoretical notions and experimental data

The essence of the inversion concept of the origin of life can be narrowed down to the following theses: (1) thermodynamic inversion is the key transformation of prebiotic microsystems leading to their transition into primary forms of life; (2) this transformation might occur only in the microsystems oscillating around the bifurcation point under far-from-equilibrium conditions. The transformation consists in the inversion of the balance “free energy contribution entropy contribution” (as well as “information contribution informational entropy contribution”), from negative to positive values. At the inversion moment, the microsystem radically reorganizes in accordance with the new negentropy (i.e. biological) way of organization. According to this concept, the origin-of-life process on the early Earth took place in oscillating hydrothermal medium. The process was taking two successive stages: (1) spontaneous self-assembly of initial three-dimensional prebiotic microsystems composed mainly of hydrocarbons, lipids, and simple amino acids, or their precursors, within the temperature interval of 100–300?°C (prebiotic stage); (2) nonspontaneous synthesis of sugars, ATP, and nucleic acids started at the inversion moment under the temperature 70–100?°C (biotic stage). Macro and microfluctuations of thermodynamic and physicochemical parameters able to sustain this way of chemical conversion have been detected in several contemporary hydrothermal systems (Kompanichenko, 2012). Conditions in potential hydrothermal medium for the origin of life were explored on the examples of several hydrothermal systems in Kamchatka peninsula. Temperature of water in hot springs ranges from?<?60 to 98?°C, in the bore holes water-steam temperature varies from?<?100 to 239?°C, and pressure from?<?1 to 35 bars at the wellheads; pH is within the interval 2.5–9.0. Pressure monitoring at the depth 950?meters in the borehole No. 30 (Mutnovsky field) has revealed high-amplitude (up to 1–2 bars) irregular macrofluctuations and low-amplitude quite regular microoscillations of pressure (amplitudes 0.1–0.3 bars). Hydrocarbons, lipid precursors, and simple amino acids are available in the fluid. The lifeless condensate of water-steam mixture (temperature 108–175?°C) contains aromatic hydrocarbons, n-alkanes, ketons, alcohols, and aldehydes. In addition to those, cycloalkanes, alkenes, dietoxyalkanes, naphtenes, fatty acids, ethyl ethers of fatty acids, and monoglycerides have been detected in hot solutions inhabited by thermophiles and hyperthermophiles (temperature 70–98?°C). According to Mukhin et al. (1979), glycine of probably abiotic origination was detected in lifeless condensate.     

Recognition of a Flipped Base in a Hairpinloop DNA by a Small Peptide

Two tiny hairpin DNAs, CORE (dAGGCTTCGGCCT) and AP2 (dAGGCTXCGGCCT; X: abasic nucleotide), fold into almost the same tetraloop hairpin structure with one exception, that is, the sixth thymine (T6) of CORE is exposed to the solvent water (Kawakami, J. et al., Chem. Lett. 2001, 258–259). In the present study, we selected small peptides that bind to CORE or AP2 from a combinatorial pentapeptide library with 2.5 × 10⁶ variants. On the basis of the structural information, the selected peptide sequences should indicate the essential qualifications for recognition of the hairpin loop DNA with and without a flipped base. In the selected DNA binding peptides, aromatic amino acids such as histidine for CORE and glutamine/aspartic acid for AP2 were found to be abundant amino acids. This amino acid preference suggests that CORE-binding peptides use π–π stacking to recognize the target while hydrogen bonding is dominant for AP2-binding peptides. To investigate the binding properties of the selected peptide to the target, surface plasmon resonance was used. The binding constant of the interaction between CORE and a CORE-binding peptide (HWHHE) was about 1.1 × 10⁶ M^?1 at 25°C and the resulting binding free energy change at 25°C (ΔG°₂₅) was ?8.2 kcal mol^?1. The binding of the peptide to AP2 was also analyzed and the resulting binding constant and ΔG°₂₅ were about 4.2 × 10⁴ M^?1 and ?6.3 kcal mol^?1, respectively. The difference in the binding free energy changes (ΔΔG°₂₅) of 1.9 kcal mol^?1 was comparable to the values reported in other systems and was considered a consequence of the loss of π–π stacking. Moreover, the stabilization effect by stacking affected the dissociation step as well as the association step. Our results suggest that the existence of an aromatic ring (T6 base) produces new dominant interactions between peptides and nucleic acids, although hydrogen bonding is the preferable mode of interaction in the absence of the flipping base. These findings regarding CORE and AP2 recognition are expected to give useful information in the design of novel artificial DNA binding peptides.     

Differential metabolic responses of perennial grass Cynodon transvaalensis×Cynodon dactylon (C₄) and Poa Pratensis (C₃) to heat stress

Differential metabolic responses to heat stress may be associated with variations in heat tolerance between cool‐season (C₃) and warm‐season (C₄) perennial grass species. The main objective of this study was to identify metabolites associated with differential heat tolerance between C₄ bermudagrass and C₃ Kentucky bluegrass by performing metabolite profile analysis using gas chromatography‐mass spectrometry. Plants of Kentucky bluegrass (Poa Pratensis‘Midnight’) and hybrid bermudagrass (Cynodon transvaalensis×Cynodon dactylon‘Tifdwarf’) were grown under optimum temperature conditions (20/15°C for Kentucky bluegrass and 30/25°C for bermudagrass) or heat stress (35/30°C for Kentucky bluegrass and 45/40°C for bermudagrass). Physiological responses to heat stress were evaluated by visual rating of grass quality, measuring photochemical efficiency (variable fluorescence to maximal fluorescence) and electrolyte leakage. All of these parameters indicated that bermudagrass exhibited better heat tolerance than Kentucky bluegrass. The metabolite analysis of leaf polar extracts revealed 36 heat‐responsive metabolites identified in both grass species, mainly consisting of organic acids, amino acids, sugars and sugar alcohols. Most metabolites showed higher accumulation in bermudagrass compared with Kentucky bluegrass, especially following long‐term (18 days) heat stress. The differentially accumulated metabolites included seven sugars (sucrose, fructose, galactose, floridoside, melibiose, maltose and xylose), a sugar alcohol (inositol), six organic acids (malic acid, citric acid, threonic acid, galacturonic acid, isocitric acid and methyl malonic acid) and nine amino acids (Asn, Ala, Val, Thr, γ‐Aminobutyric acid, IIe, Gly, Lys and Met). The differential accumulation of those metabolites could be associated with the differential heat tolerance between C₃ Kentucky bluegrass and C₄ bermudagrass.     

Oligomerization of glycine and alanine on metal(II) octacynaomolybdate(IV): role of double metal cyanides in prebiotic chemistry

Condensation reactions of amino acid (glycine and alanine) on the surface of metal(II) octacyanomolybdate(IV) (MOCMo) complexes are investigated using high-performance liquid chromatography (HPLC) and electron spray ionizations–mass spectroscopy (ESI–MS). The series of MOCMo have been synthesized and the effect of outer sphere metal ions present in the MOCMo on the oligomerization of glycine and alanine at different temperature and time found out. Formation of peptides was observed to start after 7?days at 60?°C. Maximum yield of peptides was found after 35?days at 90?°C. It has been found that zinc(II) octacyanomolybdate(IV) and cobalt(II) were the most effective metal cations present in outer sphere of the MOCMo for the production of high yield of oligomerized products. Surface area of MOCMo seems to play dominating parameter for the oligomerization of alanine and glycine. The results of the present study reveal the role of MOCMo in chemical evolution for the oligomerization of biomolecules.     

Frost tolerance and biochemical changes during hardening and dehardening in contrasting white clover populations

Successful winter survival of perennial plants, like white clover, is dependent on proper timing of both hardening and dehardening. The purpose of this study was to investigate the regulation of these processes in two cultivars (AberCrest and AberHerald) and two Norwegian ecotypes (Særheim collected at 58°46′N lat. and Bodø at 67°20′N lat.) of white clover (Trifolium repens L.). For hardening and dehardening, plants were exposed to controlled temperature conditions and frost hardiness of stolons was tested by programmed freezing at the rate of 3°C per hour. In addition, stolons were analysed for starch, soluble sugars and soluble amino acids. Cultivars AberCrest and AberHerald, selected for growth at low temperature and winter hardiness in the United Kingdom, were significantly less hardy than the Norwegian populations. After six weeks of hardening (2 weeks at 6°C and 4 weeks at 0.5°C), estimated LT₅₀ values were ?13.8, ?13.0, ?17.8 and ?20.3°C for AberCrest, AberHerald, Saerheim and Bodø, respectively. The rate of dehardening increased with increasing temperature. At low temperature (6°C), the northern ecotype from Bodø was more resistant to dehardening than AberHerald. However, at 18°C the absolute rate of dehardening (°C day^?1) was twice as high in Bodø as in AberHerald plants. Stolon elongation during dehardening was initiated at lower temperatures in AberHerald than in plants of the Bodø ecotype. The content of total soluble sugars, sucrose and the amino acids proline and arginine were significantly higher in hardy plants of Bodø than in those of AberHerald. Sucrose levels decreased during dehardening and correlations between sucrose content and LT₅₀ during this process were statistically highly significant for both Bodø and AberHerald. The least hardy populations of white clover were characterized by thick stolons, long internodes and large leaves.     

Growth,pigments, and biochemical composition of marine red alga Gracilaria crassa

The marine red alga Gracilaria crassa was investigated for its proximate composition, minerals, fatty acids, amino acids, and agar content to decipher its nutritional implications. The growth performance and pigments were studied under different combinations of temperature and salinity. On a dry weight basis the total lipid content was 1.30?±?0.05 %, protein was 5.18?±?0.64 %, carbohydrate was 42.0?±?1.2 %, ash was 43.18?±?1.15 %, and agar content was 21.52?±?0.73 %. Appreciable amounts of macro-, micro-nutrients (K?>?Na, Ca, Mg, and Fe), and essential amino acids (Ileu, His, Thr, Leu, and Lys) were found. Palmitic, stearic acid, and arachidonic acid were major fatty acids detected. The alga showed maximum daily growth rate (DGR %) 5.8?±?0.09 % at 25 °C, 35 ‰ salinity. The highest content of pigment R-phycoerythrin (444.7?±?1.9 μg g^?1 fresh weight (FW) basis) was obtained at 25 ‰ salinity at 35 °C while that of R-phycocyanin (476.3?±?2.3 μg g^?1 DW) at 30 ‰ salinity at 30 °C. This study revealed that this alga can be utilized as a potential source for food and feed. The data generated on best growth conditions will be very useful for farming of G. crassa in open sea. This alga could be used for production of natural colorants at defined control condition.     

Stability of monomeric Cro variants: Isoenergetic transformation of a type I' to a type II' beta-hairpin by single amino acid replacements

The thermodynamic stabilities of three monomeric variants of the bacteriophage lambda Cro repressor that differ only in the sequence of two amino acids at the apex of an engineered beta-hairpin have been determined. The sequences of the turns are EVK-XX-EVK, where the two central residues are DG, GG, and GT, respectively. Standard-state unfolding free energies, determined from circular dichroism measurements as a function of urea concentration, range from 2.4 to 2.7 kcal/mole, while those determined from guanidine hydrochloride range from 2.8 to 3.3 kcal/mole for the three proteins. Thermal denaturation yields van't Hoff unfolding enthalpies of 36 to 40 kcal /mole at midpoint temperatures in the range of 53 to 58 degrees C. Extrapolation of the thermal denaturation free energies with heat capacities of 400 to 600 cal/mole deg gives good agreement with the parameters determined in denaturant titrations. As predicted from statistical surveys of amino acid replacements in beta-hairpins, energetic barriers to transformation from a type I' turn (DG) to a type II' turn (GT) can be quite small.