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1.
Physicochemical studies of calf thymus chromatin were performed on micromicellar suspensions by thermal denaturation. These diluted suspensions were obtained, by a controlled shearing method, from a compact gel chromatin. Sedimentation and free-flow electrophoresis determined the size distribution of these particles. The most important result is a new transition on the melting profiles corresponding to a sudden increase of solution turbidity. This chromatin solution transition occurs at a higher temperature than usual DNA transition. The degree of « turbidity transitiondiminishes with micelle size but disappears when they are very mildly degraded by DNAases and when F 1 histone fraction is removed.This transition is not only size dependent but also depends on the micellar structure. This phenomenon is interpreted as an excluded volume effect by contact between compact and native regions of nucleoprotein micelles and denatured coils of DNA. Our study tried to show that the degree of turbidity transition can be a criterion of chromatin native structure. 相似文献
5.
Faunal remains from spoil heaps of two burrows inhabited by small carnivores (fox and badger) are analysed from a taphonomical point of view. This analysis provides characteristics for bone accumulation produced by small carnivores and will be a powerful tool for deciphering site formation about the occupational alternation of small carnivores and humans. Identified species were grouped by size classes. Faunal spectrum is composed by varied species of microfauna (70%), mesofauna (30%). Macromammal remains are under represented (less than 1%) and come from scavenged carcasses. Predators and consumed species are compared on the basis of the skeletal part representation, age classes and recording of predation marks (gnawed and digested bones). Skeletal part representation shows that all taxons exhibit a low-representation of axial skeleton and autopodial bones. Predators show a high representation of hind limb bones and a low representation of the fore limb bones whereas consumed species exhibit a reverse pattern. Mortality curve analysis provides an attritional profile for carnivores and helps for the establishment of the season of occupation of the burrow. Adults largely dominate consumed species. Moreover, predation marks are found in 1% of the carnivores’ bones and from 15% to more than 40% on prey bones. The large-sized prey bones only wear gnawed marks (20%) and anthropic marks (10–20%) whereas microfaunal remains exhibits more digested marks (40%) than gnawing stigmata (5%). Medium-sized animals bones wear both marks and with the same proportions (10–15%). 相似文献
6.
An extracellular protease has been isolated from the culture medium of Penicillium roqueforti. The enzyme was purified by precipitation with ammonium sulfate, filtration on Bio-gel P 100 columns and chromatography on D.E.A.E.-cellulose columns The purified preparation was homogenous by gel filtration on Bio-gel P 60 and electrophoretical analysis at pH 9.0 and 5.0.The protease exhibited the properties of an acid protease: the optimum pH was 3.5 for casein or hemoglobin hydrolysis and for bovine trypsinogen activation; at 40°C, the enzyme is most stable in the range of pH 3.5 to 5.5; the optimum temperatures was 50°C.E.D.T.A., D.F.P. and sulfhydryl reagents induced no inhibition.The enzyme exhibited a milk clotting activity that was fifty times weaker that the activity of rennin. Its molecular weight, estimated by gel filtration was 33 400. Amino acid composition is: Lys 15, His 2, Arg 1, Trp 5, Asp 33, Thr 27, Glu 16, Pro 10, Gly 40, Ala 25, Cys 2, Val 21, Ile 20, Leu 21, Tyr 14, Phe 19.The properties of this protease were closely similar to that of P. janthinellum and Aspergillus oryzae. 相似文献
8.
Reoxidation of the fluorescence quencher “Q” in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylureaReoxidation of the fluorescence quencher Q in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea shows the following properties: It is sensitive to very low concentrations of hydroxylamine (a few μM). It corresponds to a back reaction between Q− and the primary oxidant Z+ formed in the light. A part of this back reaction gives rise to luminescence emission. Within the range we studied the kinetic of reoxidation is second order with regards to Q−. 相似文献
10.
This paper is an attempt to describe and analyze in formal terms a genetic circuit which is rather complex and reasonably well disentangled: the control of immunity in lambdoid bacteriophages. Known models are expressed as logic equations, which relate the stade of activity of genes to variables of three kinds: genetic variables which describe the genotype of the organism, environmental variables like temperature and memorization variables. The value of each memorization variable (presence or absence of a gene product) is related to the value of the corresponding function (operation or not of the gene) by two characteristic time delays, an «establishment delay and a «decay delay.From the equations, one can derive matrices which facilitate comparison between models by showing which stable states are predicted by each model. Implications of current models, which had apparently remained cryptic, have been realized and experimentally tested.From the matrices, one can derive graphs which show the pathways (sequences of states) consistent with each model. These graphs are frequently branched and in these cases one has to analyze which conditions determine that one pathway rather than another one, is followed. 相似文献
12.
Using synchrotron radiation as the excitation light, we studied the fluorescence parameters of perylene incubated with pigeon erythrocyte membranes and with an isotropic viscous medium, the Primol 342 oil.From 4 to 37°C, we observed a single lifetime of 4.5 ns in the oil and two with the membrane (τ 1 = 1−1.4 ns and τ 2 = 5.4−6.1 ns). The dependence upon temperature of the rotation correlation time of perylene () in the oil was characteristic of an isotropic medium, whereas the limiting value of anitropy ( r ∞) was zero. With the membrane, γ ∞ decreased from 0.14 to 0.06 and from 2.9 to 0.5 ns, indicating a greater amplitude and frequency of molecular motions.The addition of chlorpromazine, indomethacine, tetracaine, n-octylamine, octanol or octanoic acid to the membrane decreased the τ 1 and τ 2 values. This would stem from the desorganization of the membrane induced by the drugs. 相似文献
14.
Methyl 2-deoxy-3,5,6-tri- O-p-nitrobenzoyl-
- ribo-hexofuranoside was converted into the glycosyl halide which was then condensed with 2,4-bis(trimethylsilyloxy)-pyrimidine in the presence of mercuric chloride to give, after alkaline methanolysis, 1-(2-deoxy-β-
- ribo-hexofuranosyl)uracil, in a yield too low for the reaction to be applied to deuterated compounds. Methyl 2-deoxy-
-allofuranoside-2- d was degraded into methyl 2-deoxy-
-arabinofuranoside-2- d. Its di- p-nitrobenzoate was converted into the glycosyl halide which was coupled with 2,4-bis(trimethylsilyloxy)-pyrimidine to give, after alkaline hydrolysis, deuterated deoxyuridine. Thiationammonolysis of a mixture of the 3′,5′-di- p-nitrobenzoates of the latter compound and its anomer gave the corresponding deoxycytidines. Comparison of the n.m.r. spectra of these compounds to that of deuterated deoxycytidine, prepared by the enzymic reduction of cytidine 5′-pyrophosphate with the Escherichia coli system in the presence of deuterium oxide confirmed that the substitution of a hydroxyl group by a hydrogen atom proceeds with retention of configuration. 相似文献
15.
Proton magnetic resonance spectra of model dipeptide molecules R 1–C′ 1O 1–N 2H 2–CHR 2–C′ 2O 2–N 3H 3–R 3 in CCl 4 solutions exhibit splited signals when investigating on mixtures of L and D enantiomers differing from the racemic composition. The major effect is observed on amide proton signals which are the ones most sensitive to the ratio of aggregation. The stereoselective dimerization of enantiomeric molecules in the so-called C5 conformational state is shown to be responsible for such a phenomenon, the intensity of which depends on the bulkiness of the side chain R 2. A theoretical approach is proposed which gives predictions in close agreement with our own experimental findings. 相似文献
16.
The statistical analysis ( Q mode) of the microfauna of 135 bottom and core samples from the Mediterranean provides evidence of the predominating local conditions in each of the two basins. Temperature, which plays a primary role in the distribution of foraminiferal species, only takes second place when one considers the regrouping of the layers. Once the temperature factor is identified, its variations provide a precise climatic curve with the advantage of not having to make any subjective interpretation of the assemblages. RésuméL'analyse en mode Q des microfaunes de 135 échantillons de Méditerrannée (niveaux de surface et carottages) met en évidence la prédominance des conditions locales propres à chacun des deux bassins. La température, qui joue un rôle primordial dans la répartition des espèces de Foraminifères, n'intervient qu'en second lieu lorsqu'on considère les regroupements des niveaux. Une fois le facteur thermique identifié, ses variations fournissent une courbe climatique précise qui présente l'avantage de ne nécessiter aucune interprétation subjective des assemblages. 相似文献
17.
Human erythrocyte phosphofructokinase was purified 150 fold by DEAE cellulose adsorption and ammonium sulfate precipitation.At pH 7,5 the enzyme exhibits allosteric kinetics with respect to ATP, fructose 6 phosphate, and Mg 2+.ATP at high concentration acted as an inhibitor and ADP, 5′AMP, 3′,5′, AMP, acted as activators. Both effectors seemed to decrease the homotropic interactions beetween the fructose 6 phosphate molecules.The activators increased the affinity of phosphofructokinase for the substrate (F6P), the inhibitor decreased it.These ligands had no effect on the maximum velocity of the reaction except in the case of ADP.Interactions between the substrates and the effector ligands on the enzyme were considered in terms of the Monod - Changeux - Wyman model for allosteric proteins.With GTP and ITP, no inhibition was observed. At saturing concentration of GTP, ATP still inhibited phosphofructokinase.Both 3′5′ AMP and fructose 6 phosphate increased the concentration of ATP required to produce an inhibition of 50 %.Citrate, like ATP, inhibited phosphofructokinase by binding most likely at the same allosteric site. Erythrocyte phosphofructokinase is inhibited by 2–3 DPG.The study of the relation log V max = f (pH) suggested, that the active center contains at least one imidazole and one sulfhydryl group. 相似文献
18.
Discriminating approach of various microplanktonic-stage contributions to whole electron transport system (ETS) measurements in sea-water sampless. b. Bacateria Data obtained from cultures of natural bacterial populations were applied to various water samples in order to determine both the phytoplanktonic and bacterial contributions to whole ETS water-sample measurements. The bacterial part was estimated both by cell enumerations and HPLC muramic-acid measurements and the phytoplankton contribution by enumeration and chlorophyll levels. An appropriate first-order equation is adequate to low carbon content samples but must be corrested for highly organic loaded samples in order to obtain a better adjustment between the sum of the “estimated” phytoplanktonic and bacterial ETS and the really-measured ETS concentrations in the water samples. 相似文献
20.
The use of the NMR spectra (250 MHz) of cellulose triacetate allows the determination of the percentage of deuterium bonded to each of the six carbon atoms of the monomer residue (except for H ?1 and one of the protons bonded to C 6 where the signals overlap). Deuterated derivatives of D -glucose and/or deuterated water were used for the biosynthesis of bacterial cellulose by Acetobacter xylinum. Analysis of NMR spectra of acetylated samples gives the following results. About 90% of the protons linked to C 1 and C 6 come from the D -glucose used in the nutrition medium, whereas 10% are exchanged with other sources of protons. Over 40% of the protons linked to C 2, C 3, C 4, and C 5 arise from the water of the nutrition medium. Discrepancies between results of biosynthesis from deuterated water and from deuterated D -glucose can only be explained if more than one enzymatic process is involved in the biosynthesis of bacterial cellulose. 相似文献
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