共查询到20条相似文献,搜索用时 125 毫秒
1.
D Richter 《Molecular & general genetics : MGG》1980,178(2):325-327
Summary The spoT gene product from Escherichia coli, the guanosine 3,5-bis(diphosphate) 3-pyrophosphohydrolase [ppGppase] catalyzes the specific release of pyrophosphate from the 3-position of guanosine 3,5-bis(diphosphate) [ppGpp]; this reaction is significantly inhibited in the presence of uncharged tRNA
yeast
Phe
. Little or no inhibition is observed with Phe-tRNAPhe, tRNAPhe-CpCpAoxi-red or ribosomal RNA (16S and 23S). 相似文献
2.
Summary Isoaccepting lysyl-tRNAs from virus-transformed cells in culture were fractionated in the RPC-5 system into peaks 1, 2, 4, 5a, 5, and 6. tRNA
6
Lys
previously was found predominantly associated with transformed cells. The codon response of each peak was determined in an E. coli ribosomal binding assay. tRNA
1
Lys
, tRNA
2
Lys
, and tRNA
4
Lys
are highly specific for the 5AAG3 codon. tRNA
5
Lys
and tRNA
5a
Lys
preferentially bind in response to AAA. tRNA
6
Lys
binds in response to AAA 3-fold better than in response to AAG. The presence of thiolated nucleosides in the anticodon regions of tRNA
5a
Lys
, tRNA
5
Lys
, and tRNA
6
Lys
is indicated by I2-inactivation of aminoacylation ability with no effect on the other isoacceptors.Functional abilities of the isoacceptors were compared in a wheat germ translational system with tobacco mosaic virus RNA as messenger. All of the isoacceptors function about equally well in translation except for tRNA
6
Lys
, which is only 14 to 24% as effective as the other isoacceptors. 相似文献
3.
Rudolf I. Salganik Rahmet I. Bersimbaev Svetlana V. Argutinskaya Elena V. Kiseleva Ninel B. Khristolyubova Victoria I. Deribas 《Molecular and cellular biochemistry》1976,12(3):181-191
Summary The regulation patterns of gastric acid secretion in rats were investigated. Pentagastrin and histamine stimulate gastric acid secretion, but the inhibitors of DNA-dependent synthesis of RNA and of proteins prevent only the pentagastrin action. It has been found that pentagastrin induces histidine decarboxylase in gastric mucosa, ensuring local accumulation of histamine. The latter activates adenylate cyclase and results in 3,5-AMP accumulation in gastric tissues. The administration of pentagastrin, histamine or 3,5-AMP enhances the activity of gastric carbonic anhydrase, the enzyme which takes part in HCI formation. The data suggest that these three compounds act sequentially (pentagastrin histamine 3,5-AMP) and the effect of the last one could be mediated through 3,5-AMP dependent protein kinase. The experiments in vitro demonstrated that gastric carbonic anhydrase can be separated into two isoenzymes and the phosphorylation of one of them by the 3,5-AMP dependent protein kinase sharply increases its activity. The findings raise the possibility that histamine and 3,5-AMP, mediating gastrin action, form together with enzymes (histidine decarboxylase, adenylate cyclase, protein kinase, carbonic anhydrase) a cascade of amplifiers.Autoradiographic studies have shown that [3H]-pentagastrin is not bound by oxyntic cells but adheres preferentially to histamine-producing-like endocrine cells and to the chief cells, while3H-histamine adheres preferentially to oxyntic and to chief cells. Electron microscopy indicates that only pentagastrin (but not histamine) initiates in-like endocrine cells ultrastructural changes characteristic for induction. Pentagastrin, histamine and 3,5-AMP administration produces in oxyntic cells ultrastructural changes typical for the secretion processes.These results lead to assumption that pentagastrin (gastrin) induces histidine decarboxylase in-like endocrine cells of gastric glands. Histamine which is secreted enhances adenylate cyclase activity in the neighbouring oxyntic cells where 3,5-AMP dependent protein kinase activates carbonic anhydrase by means of phosphorylation. These different cells form, probably, a multicellular functional unit for gastric acid secretion.An invited article. 相似文献
4.
Heise B Leppert J Wenschuh H Ohlenschläger O Görlach M Ramachandran R 《Journal of biomolecular NMR》2001,19(2):167-179
An approach to the determination of the orientation of the carbonyl chemical shift (CS) tensor in a 13C-15N-1H dipolar coupled spin network is proposed. The method involves the measurement of the Euler angles of the 13C-15N and 15N-1H dipolar vectors in the 13C CS tensor principal axes system, respectively, via a 13C-15N REDOR experiment and by a 2D relayed anisotropy correlation of the 13C CSA (2) and 15N-1H dipolar interaction (1). Via numerical simulations the sensitivity of the 1 cross sections of the 2D spectrum to the Euler angles of the 15N-1H bond vector in the 13C CSA frame is shown. Employing the procedure outlined in this work, we have determined the orientation of the 13C CS tensor in the peptide plane of the dipeptide AibAib-NH2 (Aib = -aminoisobutyric acid). The Euler angles are found to be (CN, CN) = (34° ± 2°, 88° ± 2° ) and (NH, NH) = (90° ± 10°, 80° ± 10° ). From the measured Euler angles it is seen that the 33 and 22 components of the 13C CS tensor approximately lie in the peptide plane. 相似文献
5.
We have previously reported that four tRNAs of Drosophila melanogaster randomly labeled with iodine-125 hybridize in part to the 56EF region of polytene chromosomes where 5S RNA genes occur. In the presence of a 100-fold excess of unlabeled 5S RNA no hybridization of randomly labeled 125I-tRNAAsp
2 occurred at 56EF although hybridization elsewhere was not affected. In addition, tRNAAsp
2 labeled by introducing 125I-5-iodocytidylyl residues into the 3-CCA end with tRNA nucleotidyl transferase did not hybridize to 56EF but did hybridize to its other sites. The hybridization of tRNALys
2, tRNAGly
3 and tRNAMet
3 at 56EF was not eliminated by a 25 to 100-fold excess of unlabeled 5S RNA. When these tRNAs were labeled at the -CCA terminus they hybridized to 56EF as well as to their other sites with the exception that terminally labeled tRNALys
2 no longer hybridized to 62A. The hybridization of the latter three species of tRNA to the region of the 5S genes, amongst other sites, is confirmed. The previously observed hybridization of tRNAAsp
2 in this region appears to have been due to contamination of the tRNA sample with traces of material derived from 5S RNA. 相似文献
6.
J. P. Ferris H. Yanagawa P. A. Dudgeon W. J. Hagan Jr. T. E. Mallare 《Origins of life and evolution of the biosphere》1984,15(1):29-43
Diiminosuccinonitrile (DISN) is formed readily by the Fe3+ oxidation of diaminomaleonitrile, a tetramer of HCN. DISN effects the phosphorylation of uridine in 13% yield to a mixture of the isomers of UMP when the reaction is performed in dimethylformamide solution. A 4% yield of the UMP isomers is obtained in neutral aqueous solution using 2 times the DISN concentration and 7 times the phosphate concentration used in DMF. DISN did not effect the conversion of adenosine to AMP or 5-AMP to 5-ADP in aqueous solution. The cyclization of 3-AMP and 3-UMP to the corresponding 2,3-cyclic phosphates proceeds in yields as high as 40–50% at 60°C in pH 6 aqueous solutions in the presence of divalent metal ions. Lower yields of the cyclic phosphate are observed when 2-AMP is the starting material. Substitution of acetate buffer for imidazole buffer results in a decrease in the yield of cyclic phosphate, the extent of which depends on the metal ion used in the reaction. No 3,5-cyclic AMP was detected as a reaction product with either 5-AMP or 3-AMP as the starting material except for a 2.4% yield from 3-AMP in the presence of Zn2+. BrCN effects the conversion of 3-AMP to the 2,3-cyclic AMP in 37–65% yield depending on the divalent cation used as catalyst. A mechanism has been proposed for these cyclization reactions and their potential significance to the prebiotic synthesis of ribonucleic acid derivatives is discussed.Chemical Evolution 41. For previous paper see Ferris, J.P., Hagan, W.J., Jr., Alwis, K. W., and McCrea, J.: 1982,J. Mol. Evol.
18, 304–309.Presented at the 7th International Conference on The Origins of Life, Mainz, F.R.G., 1983. 相似文献
7.
Teruo Yoshino Minobu Sadamitsu Megumi Minagawa Gerd Reuter Roland Schauer 《Glycoconjugate journal》1988,5(4):377-384
The preparation of benzyl 2,3,6,2,6-penta-O-benzyl--d-lactoside, which is a key intermediate for chemical synthesis of oligosaccharide components of glycosphingolipids, was achieved by an improved method. The 3-O-p-methoxybenzyl and 3-O-methyl derivatives were prepared from benzyl 2,3,6,2,6-penta-O-benzyl--d-lactoside through stannylation. By using benzyl -d-lactoside as starting material, benzyl 3-O-methyl-, 3-O-benzyl- and 3-O-p-methoxybenzyl--d-lactoside were regioselectively synthesized using the same procedure. 相似文献
8.
Summary Organic pyrophosphates such as UppA and NAD are formed when a solution containing a nucleotide, a nucleoside 5-polyphosphate, Mg2+ and imidazole are allowed to dry out. We suggest that this synthesis may have occured concurrently with oligonucleotide formation.Abbreviations Im
Imidazole
- CDI
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride
- EDTA
ethylenediaminetetraacetic acid
- A
adenosine
- U
uridine
- pnA
adenosine 5-poly-phosphate containing n phosphate residues
- pU
uridine 5-phosphate
- AppA
P1,P2-diadenosine 5-pyrophosphate
- UppA
P1-(uridine 5)-P2-(adenosine 5)-pyrophosphate
- ImpA
adenosine 5-phosphorimidazolide
- NMN
nicotinamide mononucleotide
- NAD
nicotinamide-adenine dinucleotide 相似文献
9.
Ahlert Schmidt 《Archives of microbiology》1977,112(3):263-270
Crude extracts of Rhodospirillum rubrum catalyzed the formation of acid-volatile radioactivity from (35S) sulfate, (35S) adenosine-5-phosphosulfate, and (35S) 3-phosphoadenosine-5-phosphosulfate. An enzyme fraction similar to APS-sulfotransferases from plant sources was purified 228-fold from Rhodospirillum rubrum. It is suggested here that this enzyme is specific for adenosine-5-phosphosulfate, because the purified enzyme fraction metabolized adenosine-5-phosphosulfate, however, only at a rate of 1/10 of that with adenosine-5-phosphosulfate. Further, the reaction with 3-phosphoadenosine-5-phosphosulfate was inhibited with 3-phosphoadenosine-5-phosphate whereas this nucleotide had no effect on the reaction with adenosine-5-phosphosulfate. For this activity with adenosine-5-phosphosulfate the name APS-sulfotransferase is suggested. This APS-sulfotransferase needs thiols for activity; good rates were obtained with either dithioerythritol or reduced glutathione; other thiols like cysteine, 2-3-dimercaptopropanol or mercaptoethanol are less effective. The electron donor methylviologen did not catalyze this reaction. The pH-optimum was about 9.0; the apparent K
m for adenosine-5-phosphosulfate was determined to be 0.05 mM with this so far purified enzyme fraction. Enzyme activity was increased with K2SO4 and Na2SO4 and was inhibited by 5-AMP. These properties are similar to assimilatory APS-sulfotransferases from spinach and Chlorella.Abbreviations APS
adenosine-5-phosphosulfate
- PAPS
3-phosphoadenosine-5-phosphosulfate
- 5-AMP
adenosine-5-monophosphate
- 3-AMP
adenosine-3-monophosphate
- 3-5-ADP
3-phosphoadenosine-5-phosphate (PAP)
- DTE
dithiorythritol
- GSH
reduced glutathione
- BAL
2-3-dimercaptopropanol 相似文献
10.
Zusammenfassung Serumproben von 1322 Blutspendern aus Hessen, 40 Familien mit 89 Kindern, 20 Mutter-Kind-Kombinationen und 268 Sera einer Bantupopulation aus Portugiesisch Angola wurden mit einer modifizierten Technik der Hochspannungs-Dünnschichtelektrophorese auf Agarosegel hinsichtlich des C3-Polymorphismus untersucht. Die Genfrequenzen für Weiße (C3S=0.779, C3F=0.215) und Neger (C3S=0.95, C3F=0,048) stimmen gut mit den Werten anderer Autoren überein. Insgesamt ließen sich bei Weißen 9 Phänotypen sicher abgrenzen, bei Negern 3. Familienstudien bestätigten den für die Allele C3S und C3F angenommenen Vererbungsmodus (autosomal codominant) ausnahmslos. Die Frage der Lagerungsstabilität des C3 wurde abschließend untersucht.
Investigations on C3-polymorphism ( 1c-Globulin)Gene frequencies and family studies in blood donors from Hessen and a Bantu population
Summary Serum samples of 1322 unrelated individuals from Hessen (Germany), 40 families with 89 children, 20 mother-child-combinations and 268 sera of a Bantu population from Angola were examined for C3 polymorphism using a modified technique of high voltage agarose gel electrophoresis. The gene frequencies for Caucasians (C3S=0.779, C3F=0.215) and negroes (C3S=0.95, CF=0.048) are in good accordance with those obtained by other authors. In total 9 different phenotypes were observed in Caucasians, 3 phenotypes in negroes. Family studies verify the supposed way of inheritance (autosomal codominant for C3S and C3F) without exception. Finally the problem of C3-inactivation by storage was investigated.相似文献
11.
Rabbit anti-mouse-Ia serum was raised against Ia specificities present in CBAJH (H-2
k) serum. This xenogeneic antiserum was considered to react with similar specificities to those detected by mouse anti-Iak alloantisera and more evidence is now presented for this contention. By absorption, the xenogeneic antiserum was found to react with spleen, lymph node, bone marrow, and thymus, reactions similar to that found with the allogeneic anti-Iak antiserum. Furthermore, red cells, platelets, brain, kidney, and liver could not absorb the activity from the xenogeneic antiserum, demonstrating the selective tissue distribution of the antigens reactive with this serum. This reactive population was previously shown to consist of B cells and a subpopulation of T cells. In a backcross study of (C57BL/6 × A)F1 × C57BL/6, the rabbit anti-Ia and mouse anti-Ia reactions were found to segregate together, and some evidence for the genetic regulation of the expression of Ia specificities was also found. By direct testing, and by absorption testing using a number of strains, the xenogeneic antiserum was shown to contain high titers of antibody to Ia.1, 3, 7, 15, and 17; lower titers to Ia.19, and 22; little antibody to Ia.18, and no reaction for the private specificity Ia. 2, although the multiple absorptions required to define these specificities may have observed some reactions. The data indicate that the xenogeneic and allogeneic anti-Iak antisera recognize similar Ia determinants, which map to theLA, IE andIC subregions of theH-2 complex. These have been given the same specificity designation as the allogeneic specificities, but they are separately identified by a prime ('). 相似文献
12.
When the leaves of Mimosa pudica are changed from their normal position in the gravitational field, they perform reversible compensatory movements by means of pulvini. These movements are not the result of growth processes but involve reversible turgor variations. These variation are concomitant with ion migrations within pulvini: during the gravitropic movement, K+ and Cl- shift towards the adaxial half of the motor organ whereas Ca2+ shifts towards the abaxial half. Compounds known to affect K+ transport, tetraethylammonium chloride and valinomycin, do not hinder the gravitropic movement but inhibit strongly the seismonastic reaction. The same general result is obtained with compounds affecting anion transport, disulfonic stilbenes and 9-anthracene carboxylic acid. Calcium chelators inhibit the gravitropic movement more efficiently than the seismonastic reaction and the calcium ionophore A 23 187 increases both movements. The data obtained with these various compounds indicate that ions do not have the same functional importance in the regulation of the two different pulvinar movements.Abbreviations abx
abaxial half of the pulvinus
- adx
adaxial half of the pulvinus
- 9-AC
9-anthracene carboxylic acid
- DIDS
4,4-diisothiocyanatostilbene-2,2-disulfonic acid
- EDTA
ethylenediaminetetraacetic acid
- EGTA
ethylene glycol-bis-(-aminoethyl ether)-N,N,N,N-tetraacetic acid
- SITS
4-acetamido-4-isothiocyanatostilbene-2,2-disulfonic acid
- TEA
tetraethylammonium chloride 相似文献
13.
James P. Ferris Kamaluddin Gözen Ertem 《Origins of life and evolution of the biosphere》1990,20(3-4):279-291
2-d-5-GMP and 2-d-5-AMP bind 2 times more strongly to montmorillonite 22A than do 2-d-5-CMP and 5-TMP. The dinucleotide d(pG)2 forms in 9.2% yield and the cyclic dinucleotide c(dpG)2 in 5.4% yield in the reaction of 2-d-5-GMP with EDAC in the presence of montmorillonite 22A. The yield of d(pC)2 (2.0%) is significantly lower but comparable to that obtained from 5-TMP. The yield of dimers which contain the phosphodiester bond decreases as the reaction medium is changed from 0.2 M NaCl to a mixture of 0.2 M NaCl and 0.075 M MgCl2. A low yield of d(pA)2 was observed in the condensation reaction of 5-ImdpA on montmorillonite 22A. The cyclic nucleotide (3,5-cdAMP) was obtained in 14% yield from 3-ImdpA. The yield of d(pA)2 obtained when EDAC is used as the condensing agent increases with increasing iron content of the Na+-montmorillonite used as catalyst. Evidence is presented which shows that the acidity of the Na+-montmorillonite is a necessary but not sufficient factor for the montmorillonite catalysis of phosphodiester bond formation. 相似文献
14.
Morishita F Shimada A Fujimoto M Katayama H Yamada K 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(7):533-540
The signal-transduction system that mediates the melanosome-aggregating response in melanophores of the black-moor goldfish, Carassius auratus, was investigated by examining the inhibition of adenylate cyclase activity mediated by -adrenoceptors in cultured cells. When the melanophores were incubated with 1 mmol·l-1 3-isobutyl-1-methylxanthine for 5 min, the intracellular level of cyclic adenosine-3,5-monophosphate increased two- to three-fold. Norepinephrine at 100 nmol·l-1 and naphazoline at 1 mol·l-1 inhibited the 3-isobutyl-1-methylxanthine-induced accumulation of cyclic adenosine-3,5-monophosphate in the cells in both the presence and the absence of isoproterenol, a -adrenergic agonist. Methoxamine and phenylephrine also reduced the extent of accumulation of cyclic adenosine-3,5-monophosphate, but only when they were present at relatively high concentrations (above 100 mol·l-1). The range of concentrations at which norepinephrine inhibited the accumulation of cyclic adenosine-3,5-monophosphate was consistent with the range at which it induced the aggregation of melanosomes. Pretreatment of the cells with pertussis toxin (1 g·ml-1) for 15 h or treatment with 100 nmol·l-1 yohimbine (an 2-adrenergic antagonist) inhibited the effects of the -adrenergic agonists on both the aggregation of melanosomes and the 3-isobutyl-1-methylxanthine-induced accumulation of cyclic adenosine-3,5-monophosphate, but prazosin (an 1adrenergic antagonist) at 100 nmol·l-1 was not inhibitory. These results indicate that the melanosome-aggregating response of the goldfish melanophore is induced mainly via inhibition of the activity of adenylate cyclase, which occurs as result of stimulation of a pathway that involves 1adrenergic and a inhibitory GTP-binding protein.Abbreviations A-kinase
cAMP-dependent protein kinase
- BSS
balanced salts solution
- CaM
calmodulin
- cAMP
cyclic adenosine-3,5-monophosphate
- Clo
clonidine
- EDTA
ethylenediaminetetra-acetic acid
- G-protein
GTP-binding protein
- HEPES
N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid
- IBMX
3-isobutyl-1-methylxanthine
- IP3
inositol 1,4,5-trisphosphate Mex, methoxamine
- MSH
melanocyte-stimulating hormone
- Nap
naphazoline
- NE
norepinephrine
- Oxy
oxymetazoline
- Phe
phenylephrine
- PTX
pertussis toxin 相似文献
15.
Robert H. Symons 《Molecular biology reports》1975,2(4):277-285
Purified cucumber mosaic virus (CMV) RNA was reacted with NaIO4 and then [3H]KBH4 to label ends containing exposed 2,3-hydroxyls. The four major RNA species were then fractionated by polyacrylamide gel electrophoresis. Analysis of digests of these RNAs by ribonucleases T1 plus T2, alkaline phosphatease, snake venom diesterase and nucleotide pyrophosphatase by means of paper electrophoresis and ion-exchange chromatography indicated that the sequence m7G(5)ppp(5)N was present at the 5-end of 75–92% of all RNA molecules. In addition, about 90% of the 3-ends terminated in either adenosine or cytidine. 相似文献
16.
Richard Holmquist 《Journal of molecular evolution》1976,8(4):337-349
Summary A nucleic acid chain L nucleotides in length, with the specific base sequence B1B2.BL, each Bi being A, G, C, or T, is defined by the L-dimensional vector B = (B1, B2, , BL), the kth position in the chain being occupied by the base Bk. Let PBB' be the twelve given constant non-negative transition probabilities that in a specified position the base B is replaced by the base B in a single step, and let P
BB'
(XX)
be the probability that the position goes from base B to B in X steps. An exact analytical expression for P
BB'
(XX)
is derived. Assuming that each base mutates independently of the others, an exact expression is derived for the probability P
BB'
(XX)
that the initial gene sequence B goes to a sequence B = (B1, B2, , BL) after X = (X1, X2, , XL) base replacements, where Xk is the number of single-step base replacements in the kth position. The resulting equations allow a more precise accounting for the effects of Darwinian natural selection in molecular evolution than does the idealized but biologically less accurate assumption that each of the four nucleotides is equally likely to mutate to and be fixed as one of the other three. Illustrative applications of the theory to some problems in biological evolution are given. 相似文献
17.
A. Banin J. G. Lawless J. Mazzurco F. M. Church L. Margulies J. B. Orenberg 《Origins of life and evolution of the biosphere》1985,15(2):77-88
The effect of adsorbed ions and pH on the adsorption of several purine and pyrimidine nucleotides on montmorillonite was studied. The cations used to prepare homoionic montmorillonite were Na+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+. The nucleotides studied were 5-, 3-, and 2-AMP, and 5-CMP in the pH range 2 through 12. The results show that preferential adsorption amongst nucleotides and similar molecules is dependent upon pH and the nature of the substituted metal cation in the clay. At neutral pH, it was observed that 5-AMP was more strongly adsorbed than 2-AMP, 3-AMP, and 5-CMP. Cu2+ and Zn2+ clays showed enhanced adsorption of 5-AMP compared to the other cation clays studied in the pH range 4–8. Below pH 4, the adsorption is attributed to cation and anion exchange adsorption mechanisms; above pH 4, anion exchange may also occur, but the adsorption (when it occurs) likely depends on a complexation mechanism occurring between metal cation in the clay exchange site and the biomolecule. It is thus proposed that homoionic clays may have played a significant role in the concentration mechanism of biomonomers in the prebiotic environment, a prerequisite step necessary for the formation of biopolymers in the remaining steps leading to the origin of life.On leave from Saegram Centre for Soil and Water Sciences, Hebrew University, Rehovot, 76100, Israel. 相似文献
18.
Kojima C Kawashima E Sekine T Ishido Y Ono A Kainosho M Kyogoku Y 《Journal of biomolecular NMR》2001,19(1):19-31
The sugar conformation of a DNA decamer was studied with proton-proton 3J coupling constants. Two samples, one comprising stereospecifically labeled 2-R-2H for all residues and the other 2-S-2H, were prepared by the method of Kawashima et al. [J. Org. Chem. (1995) 60, 6980–6986; Nucleosides Nucleotides (1995) 14, 333–336], the deuterium labeling being highly stereospecific 99% for all 2-2H, 98% for 2-2H of A, C, and T, and 93% for 2-2H of G). The 3J values of all H1-H2 and H1-H2 pairs, and several H2-H3 and H2-H3 pairs were determined by line fitting of 1D spectra with 0.1–0.2 Hz precision. The observed J coupling constants were explained by the rigid sugar conformation model, and the sugar conformations were found to be between C3-exo and C2-endo with m values of 26° to 44°, except for the second and 3 terminal residues C2 and C10. For the C2 and C10 residues, the lower fraction of S-type conformation was estimated from JH1H2 and JH1H2 values. For C10, the N–S two-site jump model or Gaussian distribution of the torsion angle model could explain the observed J values, and 68% S-type conformation or C1-exo conformation with 27° distribution was obtained, respectively. The differences between these two motional models are discussed based on a simple simulation of J-coupling constants. 相似文献
19.
A quantitative analysis of JPH scalar couplings in nucleic acids is difficult due to small couplings to phosphorus, the extreme overlap of the sugar protons and the fast relaxation of the spins involved in the magnetization transfer. Here we present a new methodology that relies on heteronuclear Constant Time Correlation Spectroscopy (CT-COSY). The three vicinal 3JPH3, 3JPH5 and 3JPH5 scalar couplings can be obtained by monitoring the intensity decay of the Pi-H3i – 1 peak as a function of the constant time T in a 2D correlation map. The advantage of the new method resides in the possibility of measuring the two 3JPH5 and 3JPH5 scalar couplings even in the presence of overlapped H5/H5 resonances, since the quantitative information is extracted from the intensity decay of the P-H3 peak. Moreover, the relaxation of the H3 proton is considerably slower than that of the H5/H5 geminal protons and the commonly populated conformations of the phosphate backbone are associated with large 3JPH3 couplings and relatively small 3JPH5 / H5. These two facts lead to optimal signal-to-noise ratio for the P-H3 correlation compared to the P-H5/H5 correlation.The heteronuclear CT-COSY experiment is suitable for oligonucleotides in the 10–15 kDa molecular mass range and has been applied to the 30mer HIV-2 TAR RNA. The methodology presented here can be used to measure P-H dipolar couplings (DPH) as well. We will present qualitative results for the measurement of P-Hbase and P-H2 dipolar couplings in the HIV-2 TAR RNA and will discuss the reasons that so far precluded the quantification of the DPHs for the 30mer RNA. 相似文献
20.
W. Giard P. Favrel E. Boucaud-Camou 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1995,164(7):518-523
The (neuro)endocrine control of enzyme release from invertebrate digestive cells remains poorly understood. A tissue dissociation procedure was developed to investigate the regulatory mechanisms of -amylase discharge from the cells of the stomach-digestive gland complex of the scallop Pecten maximus. The validity of the experimental system was tested by increasing the intracellular concentration of second messenger analogues (N
6,2-o-dibutyryl-adenosine-3,5 cyclic monophosphate and the ionophore A23187) known to mimic the activity of naturally occurring secretagogues in vertebrates: N
6,2-o-dibutyryl-adenosine-3,5 cyclic monophosphate increased the time and dose-dependent release of -amylase in a similar way as in vertebrates. A23187 was also very effective in inducing enzyme discharge. Since the in vitro bioassay was shown to be functional and because axon terminals were previously seen in close contact to -amylase secreting cells, the effect of some classic neurotransmitters was explored. Only the cholinergic agonist carbachol and dopamine evoked a secretory response. Maximal stimulation of -amylase release was reached at 10-5 mol·l-1 carbachol; at the same concentration dopamine was less effective than carbachol. By contrast, serotonin was totally inactive. The in vitro bioassay should prove useful for the identification of regulatory molecules involved in the control of enzyme discharge and to study stimulus secretion coupling mechanisms in scallop digestive cells.Abbreviations DBcAMP
N
6, 2-O-dibutyryl-adenosine-3,5 cyclic monophosphate
- cAMP
adenosine-3,5 cyclic monophosphate 相似文献