天目山柳杉树轮δ13C年序列差异

对天目山3株柳杉树轮δ¹³C年序列分别进行了测定,分析了柳杉树轮δ¹³C年序列变化的异同及其原因.结果表明,在1837～1982年的共同时段,3个树轮δ¹³C年序列彼此间相关系数为：r₁₂=0.47,r₁₃=0.65,r₂₃=0.52 (n=146),都通过了显著性水平α=0.001的信度检验.用多项式拟合法去除原δ¹³C年序列中的高频变化后,所得3个低频序列间高度正相关;原δ¹³C年序列与拟合序列的差值序列即高频序列间也显著正相关,相关系数均达到0.79～0.99,说明气候因素引起树轮δ¹³C年序列的高频变化及大气CO₂浓度引起的低频变化对不同的柳杉个体是共同的.3株树轮δ¹³C年序列间的差异主要是树木立地处局部环境条件的不同所造成的,但是局部环境条件所引起的树轮δ¹³C年序列间的个性差异对其共性变化影响较小.所以,3个树轮δ¹³C年序列间的个性差异,并不影响树轮δ¹³C年作为气候变化研究代用资料的适宜性及重建历史气候结果的可靠性与一致性.     

Solvent effect on lipase enantioselectivity. Evidence for the presence of two thermodynamic states

The enantioselectivity of lipase-catalyzed kinetic resolutions has been measured at various temperatures in binary mixtures of solvents. Varying the solvent composition and temperature had a profound effect on the enantiomeric ratio. The values for delta delta H(R-S)(#) and delta delta S(R-S)(#), calculated from the E values measured at various temperatures, were estimated as a function of the solvent composition. By plotting delta delta H(R-S)(#) versus delta delta S(R-S)(#) as a function of the solvent composition, an extreme was observed. The resulting "hairpin-type" enthalpy-entropy compensation plots can be described by assuming the presence of two thermodynamically distinct physical states, displaying different enantioselectivities, that are in equilibrium with one another. Changing the solvent composition results in a change in the equilibrium constant K(eq) for the two states. The intriguing bell-shaped curves of the enantioselectivity versus solvent composition observed for lipase-catalyzed kinetic resolutions can be described assuming a linear correlation for the logarithm of K(eq) and the solvent composition. Thus, a simulation of the two-state model adequately describes the solvent effects found for lipase-catalyzed kinetic resolutions in binary mixtures of solvents and possibly in series of homologous organic solvents.     

Diurnal variation of the delta 13C of pine needle respired CO2 evolved in darkness

The delta 13C of pine needle CO2 evolved in darkness (delta 13Cr) for slash pine trees (Pinus elliottii) was determined by placing recently collected pine needles in darkness and collecting respired CO2 over a short time period (<15 min). Delta 13Cr measurements were made over several 24 h periods to test the hypothesis that significant variation in delta 13Cr would be observed during a diurnal cycle. The delta 13Cr measurements from the 24 h time series trials showed a consistent midday 13C-enrichment (5-10 per thousand) relative to bulk biomass. The delta 13Cr values became more 13C-depleted at night and following shading, and approached bulk-biomass delta 13C values by dawn. The effect of night-time respired 13C-enriched CO2 on the delta 13C value of the remaining assimilate is shown to be minimal (13C depleted by 0.22 per thousand) under field conditions for P. elliottii needles.     

Opioid receptor affinity and selectivity effects of second residue and carboxy terminal residue variation in a cyclic disulfide-containing opioid tetrapeptide.

The previously described cyclic, delta opioid receptor-selective tetrapeptide H-Tyr-D-Cys-Phe-D-Pen-OH, where Pen, penicillamine, is beta-beta-dimethylcysteine, was modified at residues 2 and 4 by varying combinations of D- and L-Cys and D- and L-Pen, and effects on mu and delta opioid receptor binding affinities and on potency in the mouse vas deferens (MVD) smooth muscle assay were evaluated. A comparison was drawn between consequences of alterations in this series of analogs and those of analogous modifications in the related cyclic pentapeptide series which includes the highly delta receptor-selective [D-Pen2,D-Pen5]enkephalin, DPDPE. Unlike effects observed in the cyclic pentapeptide series, the mu receptor binding affinities of the cyclic tetrapeptides are not dramatically influenced by substitution of Pen for Cys at residue 2. Conversely, while binding of the pentapeptides is only slightly affected by alteration of the chirality of the carboxy-terminal residue, modification of stereochemistry at the carboxy terminus in the tetrapeptides critically alters binding behavior at both mu and delta sites. In contrast with the pentapeptide series, the tetrapeptides appear to be highly dependent upon primary sequence for binding and activity, as only the lead compound binds with high affinity to the delta site. Results suggest that the less flexible cyclic tetrapeptides, lacking the Gly3 residue, display more stringent structural requirements for binding and activity than do the corresponding cyclic pentapeptides.     

Replication of the cauliflower mosaic virus: role and stability of the cloned delta 3 discontinuity sequence

A fragment of cauliflower mosaic virus (CaMV) DNA, containing delta 3, one of the three discontinuity sequences, was cloned in various ways into CaMV DNA deleted for the delta 3 sequence. The series of constructions was monitored for the appearance of the typical single-strand (ss) discontinuity after hybrid CaMV replication in plants. The delta 3 discontinuity was observed only if the orientation of inserted DNA sequence was the same as in the wild-type virus. Long polylinker sequences used for insertion of the fragment into cloned viral DNA, affected the stability of the insert in progeny viral DNA in plants by acting as recombination targets.     

Mixed kappa agonists and mu agonists/antagonists as potential pharmacotherapeutics for cocaine abuse: synthesis and opioid receptor binding affinity of N-substituted derivatives of morphinan

A series of new N-substituted derivatives of morphinan was synthesized and their binding affinity for the three opioid receptors (mu, delta, and kappa) was determined. A paradoxical effect of N-propargyl (MCL-117) and N-(3-iodoprop-(2E)-enyl) (MCL-118) substituents on the binding affinities for the mu and kappa opioid receptors was observed. All of these novel derivatives showed a preference for the mu and kappa versus delta binding.     

Microsomal delta 8,14-sterol delta 14-reductase in higher plants. Characterization and inhibition by analogues of a presumptive carbocationic intermediate of the reduction reaction

An enzymatic assay for delta 8,14-sterol delta 14-reductase, an enzyme involved in sterol biosynthesis, has been developed for the first time in higher plants. The properties of the microsomal enzyme have been established with respect to cofactor requirements, kinetics and substrate specificity. This enzymatic double-bound reduction is thought to proceed through an electrophilic addition mechanism, involving a C14 putative carbonium ion high-energy intermediate. Using this in vitro assay, ammonium and iminium analogues of this cationic intermediate were shown to be potent inhibitors of the reduction reaction. Thus, compounds of the N-alkyl-8-aza-4 alpha,10-dimethyl-trans-decal-3 beta-ol series strongly inhibited sterol reductase (I50 = 0.07 - 4 microM) (I50/Km = 10(-4) - 10(-3), as did the antimycotic agent 15-azasterol (I50 = 0.03 microM); all of these compounds act as reaction-intermediate analogues of the proposed C14 carbonium ion intermediate. Moreover, the in vitro inhibition of the plant sterol reductase by a series of ammonium-ion-containing fungicides was demonstrated. The relative specificity of these different series of inhibitors toward cycloeucalenol-obtusifoliol isomerase, delta 8----delta 7-sterol isomerase and delta 8,14-sterol delta 14-reductase, was directly studied.     

Pharmacophore elements of the TIPP class of delta opioid receptor antagonists

Summary A series of tri-and tetrapeptides sharing the amino-terminal dipeptide unit Tyr-Tic, found in the high-affinity delta opioid receptor antagonist Tyr-Tic-Phe-Phe (TIPP), was prepared and evaluated in receptor binding assays to explore the role(s) of the phenylalanine residues in positions 3 and 4. It was found that aromaticity of residues 3 and 4 is not required for high affinity, a lipophilic side chain in either location being sufficient, as evidenced by the high delta receptor binding affinities observed for the tetrapeptide Tyr-Tic-Ala-Leu and the tripeptide Tyr-Tic-Leu. These results support the suggestion of Temussi et al. [Biochem. Biophys. Res. Commun., 198 (1994) 933] that the aromatic side chain of the Tic residue corresponds to the aromatic side chain found in residues 3 or 4 in other delta-selective peptide series.     

Synthesis and binding affinities of 4-diarylaminotropanes, a new class of delta opioid agonists

A series of 4-diarylaminotropanes has been prepared. Both endo and exo diastereomeric forms bound to the delta opioid receptor but the endo isomers were more potent and selective versus the mu opioid receptor than the exo isomers. The most potent delta opioid agonist (14) exhibited a delta opioid Ki of 0.2 nM and was 860-fold selective over mu.     

Thermal unfolding of staphylococcal nuclease and several mutant forms thereof studied by differential scanning calorimetry.

The effects of eight mutations on the thermodynamics of the reversible thermal unfolding of staphylococcal nuclease have been determined over a range of pH and protein concentration by means of differential scanning calorimetry. Variation of the protein concentration was included in our study because we found a significant dependence of the thermodynamics of protein unfolding on concentration. Values for the change in the standard free energy of unfolding, delta delta G0d, produced by the mutations in the pH range 5.0-7.0 varied from 1.9 kcal mol-1 (apparent stabilization) for H124L to -2.8 kcal mol-1 (apparent destabilization) for L25A. As has been observed in numerous other cases, there is no correlation in magnitude or sign between delta delta G0d and the corresponding values for delta delta Hd and T delta delta S0d, the latter quantities being in most cases much larger in magnitude than delta delta G0d. This fact emphasizes the difficulty in attempting to correlate the thermodynamic changes with structural changes observed by X-ray crystallography.     

Analysis of mRNA decay and rRNA processing in Escherichia coli multiple mutants carrying a deletion in RNase III.

RNase III is an endonuclease involved in processing both rRNA and certain mRNAs. To help determine whether RNase III (rnc) is required for general mRNA turnover in Escherichia coli, we have created a deletion-insertion mutation (delta rnc-38) in the structural gene. In addition, a series of multiple mutant strains containing deficiencies in RNase II (rnb-500), polynucleotide phosphorylase (pnp-7 or pnp-200), RNase E (rne-1 or rne-3071), and RNase III (delta rnc-38) were constructed. The delta rnc-38 single mutant was viable and led to the accumulation of 30S rRNA precursors, as has been previously observed with the rnc-105 allele (P. Gegenheimer, N. Watson, and D. Apirion, J. Biol. Chem. 252:3064-3073, 1977). In the multiple mutant strains, the presence of the delta rnc-38 allele resulted in the more rapid decay of pulse-labeled RNA but did not suppress conditional lethality, suggesting that the lethality associated with altered mRNA turnover may be due to the stabilization of specific mRNAs. In addition, these results indicate that RNase III is probably not required for general mRNA decay. Of particular interest was the observation that the delta rnc-38 rne-1 double mutant did not accumulate 30S rRNA precursors at 30 degrees C, while the delta rnc-38 rne-3071 double mutant did. Possible explanations of these results are discussed.     

新疆阿勒泰地区近440年来大气δ^13C变化

化石燃料的大量使用和森林的过度砍伐,引起大气中CO₂浓度的大幅度增加,同时由于Suess效应,大气CO₂中的δ¹³C在不断地下降．植物中δ¹³C的变化是大气CO₂浓度和同位素比值变化的敏感指示器．文中利用树木年轮δ¹³C序列和植物碳同位素分馏模型,尝试恢复了新疆阿勒泰地区近440年来大气δ¹³C的变化．结果表明,1850年之前,从树木年轮δ¹³C序列恢复的大气δ¹³C相对恒定在-6．60％0(R²=0．052),而1850年之后,该大气δ¹³C明显降低(R²=0．65)。平均约为-7．04‰,平均年降低0．0084‰．这一结果高于从冰芯气泡所恢复的大气δ¹³C,1850年～1981年冰芯大气δ¹³C平均年降低约0．0065‰．这可能与从树木年轮δ¹³C序列恢复的大气δ¹³C有更高的分辨率及树木生长点大气δ¹³C不同于全球大气δ¹³C值有关．     

Stability mutants of staphylococcal nuclease: large compensating enthalpy-entropy changes for the reversible denaturation reaction

By use of intrinsic fluorescence to determine the apparent equilibrium constant Kapp as a function of temperature, the midpoint temperature Tm and apparent enthalpy change delta Happ on reversible thermal denaturation have been determined over a range of pH values for wild-type staphylococcal nuclease and six mutant forms. For wild-type nuclease at pH 7.0, a Tm of 53.3 +/- 0.2 degrees C and a delta Happ of 86.8 +/- 1.4 kcal/mol were obtained, in reasonable agreement with values determined calorimetrically, 52.8 degrees C and 96 +/- 2 kcal/mol. The heat capacity change on denaturation delta Cp was estimated at 1.8 kcal/(mol K) versus the calorimetric value of 2.2 kcal/(mol K). When values of delta Happ and delta Sapp for a series of mutant nucleases that exhibit markedly altered denaturation behavior with guanidine hydrochloride and urea were compared at the same temperature, compensating changes in enthalpy and entropy were observed that greatly reduce the overall effect of the mutations on the free energy of denaturation. In addition, a correlation was found between the estimated delta Cp for the mutant proteins and the d(delta Gapp)/dC for guanidine hydrochloride denaturation. It is proposed that both the enthalpy/entropy compensation and this correlation between two seemingly unrelated denaturation parameters are consequences of large changes in the solvation of the denatured state that result from the mutant amino acid substitutions.     

Design, synthesis, and evaluation of a novel series of alpha-substituted phenylpropanoic acid derivatives as human peroxisome proliferator-activated receptor (PPAR) alpha/delta dual agonists for the treatment of metabolic syndrome

A series of alpha-alkyl-substituted phenylpropanoic acids was prepared as dual agonists of peroxisome proliferator-activated receptors alpha and delta (PPARalpha/delta). Structure-activity relationship studies indicated that the shape of the linking group and the shape of the substituent at the distal benzene ring play key roles in determining the potency and the selectivity of PPAR subtype transactivation. Structure-activity relationships among the amide series (10) and the reversed amide series (13) are similar, but not identical, especially in the case of the compounds bearing a bulky hydrophobic substituent at the distal benzene ring, indicating that the hydrophobic tail part of the molecules in these two series binds at somewhat different positions in the large binding pocket of PPAR. alpha-Alkyl-substituted phenylpropanoic acids of (S)-configuration were identified as potent human PPARalpha/delta dual agonists. Representative compounds exhibited marked nuclear receptor selectivity for PPARalpha and PPARdelta. Subtype-selective PPAR activation was also examined by analysis of the mRNA expression of PPAR-regulated genes.     

Thermodynamics of single-stranded RNA binding to oligolysines containing tryptophan.

The equilibrium binding to the synthetic RNA poly(U) of a series of oligolysines containing one, two, or three tryptophans has been examined as a function of pH, monovalent salt concentration (MX), temperature, and Mg2+. Oligopeptides containing lysine (K) and tryptophan (W) of the type KWKp-NH2 and KWKp-CO2 (p = 1-8), as well as peptides containing additional tryptophans or glycines, were studied by monitoring the quenching of the peptide tryptophan fluorescence upon binding poly(U). Equilibrium association constants, K(obs), and the thermodynamic quantities delta G(o)obs, delta H(o)obs, and delta S(o)obs describing peptide-poly(U) binding were measured as well as their dependences on monovalent salt concentration, temperature, and pH. In all cases, K(obs) decreases significantly with increasing monovalent salt concentration, with (delta log K(obs)/delta log [K+]) = -0.74 (+/- 0.04)z, independent of temperature and salt concentration, where z is the net positive charge on the peptide. The origin of these salt effects is entropic, consistent with the release of counterions from the poly(U) upon formation of the complex. Upon extrapolation to 1 M K+, the value of delta G(o)obs is observed to be near zero for all oligolysines binding to poly(U), supporting the conclusion that these complexes are stabilized at lower salt concentrations due to the increase in entropy accompanying the release of monovalent counterions from the poly(U). Only the net peptide charge appears to influence the thermodynamics of these interactions, since no effects of peptide charge distribution were observed. The binding of poly(U) to the monotryptophan peptides displays interesting behavior as a function of the peptide charge. The extent of tryptophan fluorescence quenching, Qmax, is dependent upon the peptide charge for z less than or equal to +4, and the value of Qmax correlates with z-dependent changes in delta H(o)obs and delta S(o)obs(1 M K+), whereas for z greater than or equal to +4, Qmax, delta H(o)obs, and delta S(o)obs (1 M K+) are constant. The correlation between Qmax and delta H(o)obs and delta S(o)obs(1 M K+) suggests a context (peptide charge)-dependence of the interaction of the peptide tryptophan with poly(U). However the interaction of the peptide tryptophan does not contribute substantially to delta G(o)obs for any of the peptides, independent of z, due to enthalpy-entropy compensations. Each of the tryptophans in multiple Trp-containing peptides appear to bind to poly(U) independently, with delta H(o)Trp = -2.9 +/- 0.7, although delta G(o)Trp is near zero due to enthalpy-entropy compensations.(ABSTRACT TRUNCATED AT 400 WORDS)     

Confined and unconfined stress relaxation of cartilage: appropriateness of a transversely isotropic analysis.

Previous studies have shown that stress relaxation behavior of calf ulnar growth plate and chondroepiphysis cartilage can be described by a linear transverse isotropic biphasic model. The model provides a good fit to the observed unconfined compression transients when the out-of-plane Poisson's ratio is set to zero. This assumption is based on the observation that the equilibrium stress in the axial direction (deltaz) is the same in confined and unconfined compression, which implies that the radial stress deltar = 0 in confined compression. In our study, we further investigated the ability of the transversely isotropic model to describe confined and unconfined stress relaxation behavior of calf cartilage. A series of confined and unconfined stress relaxation tests were performed on calf articular cartilage (4.5 mm diameter, approximately 3.3 mm height) in a displacement-controlled compression apparatus capable of measuring delta(z) and delta(r). In equilibrium, delta(r) > 0 and delta(z) in confined compression was greater than in unconfined compression. Transient data at each strain were fitted by the linear transversely isotropic biphasic model and the material parameters were estimated. Although the model could provide good fits to the unconfined transients, the estimated parameters overpredicted the measured delta(r). Conversely, if the model was constrained to match equilibrium delta(r), the fits were poor. These findings suggest that the linear transversely isotropic biphasic model could not simultaneously describe the observed stress relaxation and equilibrium behavior of calf cartilage.     

Kinetic and thermodynamic characterization of the R17 coat protein-ribonucleic acid interaction

A filter retention assay is used to examine the kinetic and equilibrium properties of the interaction between phage R17 coat protein and its 21-nucleotide RNA binding site. The kinetics of the reaction are consistent with the equilibrium association constant and indicate a diffusion-controlled reaction. The temperature dependence of Ka gives delta H = -19 kcal/mol. This large favorable delta H is partially offset by a delta S = -30 cal mol-1 deg-1 to give a delta G = -11 kcal/mol at 2 degrees C in 0.19 M salt. The binding reaction has a pH optimum centered around pH 8.5, but pH has no effect on delta H. While the interaction is insensitive to the type of monovalent cation, the affinity decreases with the lyotropic series among monovalent anions. The ionic strength dependence of Ka reveals that ionic contacts contribute to the interaction. Most of the binding free energy, however, is a result of nonelectrostatic interactions.     

Novel Dmt-Tic dipeptide analogues as selective delta-opioid receptor antagonists

A series of Dmt-Tic analogues with substitution on the Tic aromatic ring has been synthesized and evaluated for opioid receptor affinity and activation. Incorporation of large hydrophobic groups at position 7 of Tic did not greatly alter the delta opioid receptor binding affinities of the dipeptides whereas substitution at position 6 substantially diminished their affinity. These modified Dmt-Tic peptides showed binding affinities as low as 2.5 nM with up to 500-fold selectivity for the delta versus mu opioid receptor and proved to be delta receptor antagonists.     

Comparison of the energetics of lactose active transport: artificial versus enzyme-associated energy source

To further consider the thermochemical method as a useful approach for active transport research and to investigate the characteristic of a proton electrochemical potential (delta mu H+) across the membrane, the energetics of lactose active transport across Escherichia coli membrane vesicles coupled with an artificial electron donor (phenazine methosulfate-ascorbate) has been investigated. The results were compared with those obtained with an enzyme-associated electron donor (lactate dehydrogenase-D-lactate). The oxidation of an electron donor provided the energy necessary for the transport process. The observed higher heat of ascorbate oxidation reaction in the presence of a proton ionophore (carbonyl cyanide m-chlorophenylhydrazone) further confirmed the formation of delta mu H+ across the membrane. Part of the oxidation energy was utilized to form delta mu H+. Comparison of the energetics revealed that the magnitudes of delta Hox (the enthalpy of the oxidation reaction) and delta Hm (the enthalpy of the formation of delta mu H+) in the two energy sources were comparable (-46 kcal/mol of ascorbate to -40 kcal/mol of D-lactate for delta Hox and 9.6 kcal/mol of ascorbate to 14 kcal/mol of D-lactate for delta Hm). Comparable and low value (about 1%) was also found in the free energy transfer (defined by delta Gm/delta Gox) from the oxidation reaction to the formation of delta mu H+. These results, in combination with the close values of delta mu H+ observed in the two systems, suggested that the characteristic of the created delta mu H+ was independent of the energy source. Examination of delta Hm might provide the information on the ratio of the number of protons produced, as 1 mol of two different electron donors was oxidized. The oxidation reaction in the presence of membrane vesicles was discussed.