BIOLOGICAL FUNCTIONS OF MODIFIED NUCLEOTIDES IN tRNA MOLECULES (Ⅲ)——SYNTHESIS AND BIOLOGICAL ACTIVITY OF ANALOGS OF YEAST ALANYL tRNA WITH m~1I_(37) REPLACED BY A, G OR C

A thirty-nine nucleotide fragment (nucleotides 38—76) of yeast alanyl tRNA was prepared by using calf spleen phosphodiesterase to delete C_(36)m~1I_(37) from the 3′-half molecule of this tRNA under controlled conditions. Analogs of yeast alanyl tRNA with A, G or C instead of m~1I_(37) were synthesized and their biological activities determined. The results indicated that the aminoacylation activity of these analogs was not affected in the rat liver aminoacyl-tRNA synthetase system, compared with natural yeast alanyl tRNA. However, the incorporation activity (i. e. the activity of transferring alanine into proteins) of these analogs was significantly reduced to 20—30% of that of natural yeast alanyl tRNA in the rabbit reticulocyte lysate cell-free protein synthesizing system.     

SYNTHESIS AND DETERMINATION OF THE BIOLOGICAL ACTIVITIES OF YEAST ALANINE tRNA ANALOGUES

The role of base modification in yeast tRNAAl(?) function in protein synthesis was examined by the use of unmodified tRNA analogues. Unmodified full length tRNAs, 5'-half tRNAs (nucleotides 1-35) and 3'-half tRNAs (nucleotides 37-75) were transcribed in vitro using T7-RNA polymerase. Unmodified tRNA half molecules were joined to normally modified half molecules (5'-half, nucleotides 1-36; 3'-half, nucleotides 36-75) by T4-RNA ligase. Using this method, we synthesized three analogues of yeast tRNAAl(?): (i) tRNAAl(?) which lacks base modifications in the 5'-half of the molecule; (ii) tRNAAl(?) which lacks base modifications in the 3'-half of the molecule; and (iii) tRNAAla completely lacking base modifications. We determined the biological activities of these analogues. In rat aminoacyl-tRNA synthetase reactions, the alanine acceptance activity decreased by 52%, 79% and 85% when modified bases were absent from the 5'-half molecule, the 3'-half molecule or the total molecule, respectively. In rabbit retic     

ASSAY OF BIOLOGICAL ACTIVITY OF SYNTHETIC YEAST ALANINE TRANSFER RNA (tRNA_y~(Ala))

The biological activity of the synthetic tRNA_y~(Ala) was studied with an extremely sensitive method, tRNA_y~(Ala). accepted alanine in the presence of rat liver aminoacyl-tRNA_y~(Ala)-synthetase (this was called the accepting actvity). The aminoacylated tRNA_y~(Ala) was conveniently precipitated by ethanol with good recovery. The efficiency of transferring alanine from the aminoacylated tRNA_y~(Ala) into the protein was determined in in vitro rabbit reticulocyte lysate cell-free protein-synthesizing system (this was called the incorporation activity). Both accepting and incorporation activities could be determined in one assay with only 5-7 pmoles of tRNA_y~(Ala) either in ligation mixture or in purified form.Our results show that the accepting activities of the synthetic products were 51.6-65.6% and 91.3-106.0% of that of natural and reconstituted natural tRNA_y~(Ala) respectively. The efficiency of the incorporation of alanine in the aminoacylated tRNA_y~(Ala) into the protein was 61.6-63.1%, corresp     

SYNTHESIS OF THE 5'-HALF MOLECULE OF YEAST ALANINE tRNA

In this paper, we report the synthesis of the 5'-half molecule of yeast alanine tRNA (tRNA_y~(Ala)) by ligating three oligonucleotide fragments corresponding to the nucleotide sequences 1-13, 14-22 and 23-35 respectively under the catalysis of T_4 RNA ligase (Fig. 1). Because of the high purity of the oligonuclcotide fragments and the excellent quality of T_4RNA ligase and polynucleotide kinase we prepared, the isolation steps were simplified and the overall yields were much higher. The ligating yield of the docosamer (Ⅳ) was 75%, that of the pentatriacontamer (Ⅴ), 90%, and the isolated yield of the final product was 21% calculated on the basis of the tridecamer (Ⅲ) used in the. first reaction. Under the action of T_4 RNA ligase the synthetic 5'-half molecule was joined with the natural 3'-half molecule forming a semi-synthetic tRNA_y~(Ala), which possessed the biological activities of both accepting (~3H)-alanine and incorpprating it into proteins. The correctness of the structure of the synthetic 5     

TOTAL SYNTHESIS OF Trichosanthes TRYPSIN INHIBITOR AND ITS ANALOGUE

Trichosanthes trypsin inhibitor (TTI) is a peptide consisting of 27 amino acid residues with three pairs of disulfide bonds. This paper reports the total synthesis and disulfide bond refolding of this inhibitor and its analogue. After purification, the amino acid sequence and stoichiometrical inhibitory activity against trypsin of the synthetic inhibitor were compatible with those of the natural inhibitor. The analogue of this inhibitor in which residue Met in position 6 was replaced by Ala was also synthesized. The antitrypsin activity of this synthetic analogue was also approximate to that of the natural inhibitor.     

TOTAL SYNTHESIS OF YEAST ALANINE TRANSFER RIBONUCLEIC ACID

By a combination of chemical and enzymatic methods, small oligonucleotides with lengths varying from 2 to 8 nucleotides were synthesized from mononucleotides. The small oligonucleotides were then ligated with T_4 RNA ligase into six laxge ligonucleotides (9 to 19 nucleotides long) which were further ligated to form two half molecules with 35 and 41 nucleotides respectively, Finally, the two synthetic half molecules were annealed and ligated to obtain the whole molecule of yeast alanine tRNA (tRNA_y~(Ala)). Prior to this, two semi-syntheses were performed, i. e. ligation of the synthetic 5'-half molecule with the natural 3'-half molecule and that of the natural 5'-half molecule with the synthetic 3'-half molecule.     

ISOLATION AND PROPERTIES OF L-AMINO ACID OXIDASE FROM OPHIOPHAGUS HANNAH VENOM

This paper reports the isolation and some properties of L-amino acid oxidase from Ophi-ophagus hannah venom. The differences between L-amino acid oxidase from Ophiophagusohannah and that from other sources in specific activity, properties and the spectrum of iso-zymes are noticeable. The result of electrophoresis on polyacrylamide gel shows that this purified enzyme ishomogenous. The molecular weight determined by gradient polyacrylamide gel slab (4--30%)is around 15×10~4 dalton. The molecular weight of the subunit determined by SDS gradient gelelectrephoresis (4--30%) is around 7.3×10~4 dalton. Therefore, this enzyme is composed of twosubunits. The absorption spectrum reveals that there are two FADs in each molecule. The optimum pH of enzymic reaction is around 8.7--9.0 when L-leucine is used as substrate.The inhibition of the preducts is noticeable when substrate concentration goes beyond 3mM.This enzyme is heat stable and its activity would not decrease obviously after heating at 55℃for 40 min. A linear relationship between enzyme concentration and reaction rate was noticedwhen enzyme concentration was below 5.7μg/ml.     

STUDIES ON THE MECHANISM OF INDIRUBIN ACTION IN THE TREATMENT OF CHRONIC GRANULOCYTIC LEUKEMIA——V.BINDING BETWEEN INDIRUBIN AND DNA AND IDENTIFICATION OF THE TYPE OF BINDING

The binding between indirubin and calf thymus DNA in vitro has been verified by meansof the isotope labelling method, spectrophotometric method and thermal denaturation meas-urements. The λ_max 207 nm of indirubin shifted toward longer wave length with decrease ofabsorbance after the incubation of indirubin with DNA. The escalation of Tm value of DNAinduced by indirubin was about 2.4°C and it was reproducible. The binding force between themwas rather weak, as indirubin molecules were easily released during the precipitation withalcohol or the gel filtration. The binding was not affected by sodium chloride even at high con-centration but greatly decreased (to 20-30% of the control) in the presence of 8 M urea.These results showed that the binding between indirubin and DNA might be of hydrogen bondrather than ionic. The amount of bound ~3H-indirubin was directly proportional to the con-centration of indirubin. However, it increased abruptly when the concentration of indirubinreached 1.5×10~(-4) M. This     

SPONTANEOUS POTENTIALS OF EMBRYONIC EPITHELIUM IN URODELES (CYNOPS ORIENTALIS)

The spontaneous potentials (SPs) of nerveless embryonic epithelium of Cynops orientaliswere observed by conventional intracellular micro-electrode technique. The amplitude and fre-quency of SPs of epithelial cells and the course of initiation and decline were recorded. TheSPs can occur repeatedly at the stages when the embryonic epithelium is able to conduct exci-tation. The SP is very similar to the evoked propagatable potential, but has shorter duration.The amplitudes and frenquencies of SPs differ in the different embryos and in differentepithelial cells in the same embryo. The excitable epithelial cells of the embryo may lose theirconductivity when the SPs come to a stable phase both in amplitude and frequency. And theconductivity can recover again after the subsiding of SPs. The SPs can be eliminated by tetro-dotoxin (TTX), but they are not affected by the treatment of cobalt chloride.     

CHEMICAL SYNTHESIS AND CLONING OF SECRETIN GENE

A DNA duplex coding for the 27 amino acids of secretin has been synthesized and cloned. Indesigning the sequence of the gene, computer analysis has been applied. The following factors have beenconsidered: selection of codon usage in favour of expression in yeast; design of various sites useful ingene cloning, gene modification and expressed product purification; avoiding the repeat sequences whichmay interfere in the ligation of the synthetic fragments. The synthesis involved preparation of 12 oligo-deoxyribonucleotides (12-mer to 24-mer in length) by phosphate triester and phosphite triester method,purification by polyacrylamide gel electrophoresis (PAGE). A new plasmid pWS1 was constructed by inser-tion of the enzymatic ligated gene fragment into plasmid pWR13.     

A Thermodynamic Analysis on the Catalytic Combustion of Methane

Chemical equilibria involving 10 species and adiabatic reaction temperature of methane com-bustion in air under various conditions have been calculated in detail by means of total Gibbs energyminimization of the system. The calculation data show that the adiabatic combustion temperature of CH_4and air at stoichiometric ratio is up to about 2200 K, and the equilibrium concentration of NO is about0.0018, however that of NO_2 is only 1×10~(-6). A large amount of carbon deposition emerges when the CH_4concentration is above 26.5%. The NO and NO_2 appear only when the CH_4 concentration is below 16%.The maximum equilibrium concentrations of NO and NO_2 are 0.0028 and 2×10~(-6) respectively, at about8%CH_4 concentration. The NO and NO_2 concentrations increase with the system temperature at a lowCH_4 concentration. However, both of them can be decreased when CO_2 or steam is introduced into thesystem, which also decreases the adiabatic combustion temperature. The decrease in adiabatic tempera-ture caused by     

DYNAMIC PROCESS OF VALENCE CHANGE OF EUROPIUM ION IN EUROPIUM DIFLUORIDE AT HIGH TEMPERATURE

The dynamic process of the ionic valence changing from Eu~(2+) to Eu~(3+) in EuF_2 at high temperature has been investigated by ESCA, high,temperature X-ray diffraction, high temperature spectrum, high temperature magnetic Isusceptibility and Mssbauer spectrum. It has been shown that the formed Eu~(3+) exists in different compounds when EuF_2 is heated to high temperature in different atmospheres. In air, Eu~(3+) exists in the form of hexagonal EuOF, in nitrogen, in the form of orthogonal EuF_3 and non-hexagon EuOF. This is because decomposition or disproportionation of EuF_2 is different with different atmospheres. The magnetic susceptibility measurement showed quantitatively that the change rate from Eu~(2+) to Eu~(3+) is about 95% in air, and about 75% in nitrogen when it is heated to 900℃. A small amount of Eu~(2+) coexists with Eu~(3+) in the final product.     

SYNTHESIS OF THE COPOLYMERS OF p-DIETHYNYLBENZENE WITH OTHER ACETYLENIC DERIVATIVE S INITIATED BY (Ph_3P)_2 PdCl_2

The copolymerization of p-diethynylbenzene (PDEB) with phenylacetylene (PhA), 4, 4'-diethynylbiphenyl (DEBP)or m-diethynylbenzene (MDEB) are studied by varying mole ratios of monomers. When the mole ratios of PDEB/PhA are less or equal to 1/5, the copolymers are soluble and fusible, but the other copolymers are insoluble and infusible. The results show that the good solvent of cross-linked copolymers is benzene and their solubility parameter is 9.15 cal~(0.5).cm(-1.5). And their swellability (θ_p), Huggins parameter (χ), density (d_4~(25)) and the average molecular weights between crosslinks (c) are measured. It is found that θp and c of copolymers are greater but d_4~(25) is less than that of respective homopolymers. IR spectra show that the copolymers have transoid configuration and small number of unreacted ethynyl groups exist in the copolymers. The mechanism about the polymerization or acetylenic derivatives initiated by (Ph_3P)_2PdCl_2 is discussed.     

Dynamics simulation on the associative properties of amphiphilic functional monomer modified polyacrylamide copolymers

A kind of amphiphilic functional monomer was selected to modify polyacrylamide(PAM) or partially hydrolyzed polyacrylamide(HPAM). The relative properties of the modified polyacrylamide(HM-PAM) and modified partially hydrolyzed polyacrylamide(HM-HPAM) such as radius of gyration(Rg), hydrodynamic radius(RH), and radial distribution functions(RDFs) have been studied to find the intrinsic relation between the microstructure of the polymer chain and the intrinsic viscosities with changing the amount of modified monomers from 1% to 4%. The simulation results show that, compared to HPAM, HM-HPAM has a better performance in increasing viscosity when the percentage of modified monomers is 2% and has a stronger salt tolerance when the modified monomers is 4%. Furthermore, a complex hydrogen bonding network was revealed with the analysis of radial distribution functions(RDFs) and the pair correlation function was used to investigate the diffusivity of Na+ and carbon atoms in the COO― group.     

Mg~(2 )-MEDIATED CHANGE IN LIPID FLUIDITY ENHANCES THE RECONSTITUTED H~ -ATPASE ACTIVITY

The results by using ANS fluorescent probe and spin labels 5-NS show that the fluidity of L.(H~ -ATPase) Mg~(2 ) (H~ -ATPase from pig heart mitochondria reconstituted in the presence of Mg~(2 )) is less than that of L (H~ -ATPase)-Mg~(2 ) (proteoliposome reconstituted in the absence of Mg~(2 )). But no significant difference in fluidity has been observed when both reconstituted systems were monitored by using spin labels 12-NS and 16-NS. This indicates that Mg~(2 ) may cause changes in fluidity of the lipid molecules near the surfaces of the bilayers, but does not affect significantly the fluidity of the deeper layer of the reconstituted system.It is tentatively supposed that in the presence of Mg~(2 ), enhancement of activities of reconstituted H~ -ATPase may be due to the Mg~(2 )-mediated change in physical state of the lipids in the more superficial region of lipid bilayers so as to ensure a suitable conformation of ATPase complex, thereby possessing higher activity.     

DYNAMIC PROPERTIES OF MAIN SOUNDER IN BLACK CICADA (C. atrata Fabricius)~*

In this paper, the dynamic properties of the main sounder (the sounding muscle (SMc) and the sounding membrane (SM)) and the generating mechanism of amplitude-modulation pulse train (AMPT) are given. The acting process of SMc is a quasi-simple harmonic contraction vibration. The amplitudes of soundless and sounding contracting motion are about 17.2 /μm and 29.4/μm, respectively, and the efficiency of dynamic sounding is about 17％, The unsounded motion of SM is a quasi-simple harmonic vibration, and the amplitude is about 7.81/μm. The sounding motion of SM is a complex vibration, and the amplitude is about 12.66 μm. In each syllable of the song, AMPT_(1,2,3) are separately produced by driving vibrations (V_1,2,3)) of three long ribs in the upper half of SM, and the peaks of V_(1,2,3) lead the first pulse of high amplitude in AMPT_(1,2,3) by 0.156 ms, respectively. The membrane structure in the lower half of SM is mainly to transmit contracting movement of SMc.     

SYNTHESIS AND PROPERTIES OF POLYMERIC BIS (ETHYLENEDITHIO)-TETRATHIAFULVALENES

A polymer containing bis(ethylenedithio)-tetrathiafulvalene moiety wassynthesized and its electrochemical properties were studied by cyclic voltammetry. Thecharge transfer complexes of the polymer with TCNQ and I_2 were obtained by chemicaloxidation in dichlorobenzene. All of them are semi-conductors. A film of the polymer wasobtained by casting. Its conductivity, after oxidation with iodine, is 2.24×10~(-6)S·cm~(-1)and its conducting state is stable in air.     

DECARBOXYLATION DURING THE FORMATION OF THE FLUORESCENT NAD DERIVATIVE OF D-GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE

During the formation of the fluorescent NAD derivative of rabbit muscle D-glyceral-dehydc-3-phosphate dehydrogenase modified with ~(14)C-1-iodoacetate by ultraviolet irradiation about 1/2 of the total radioactivity is removed as CO_2, when the fluorescent intensity has reached a maximum, With a weak light source, it can be shown that the formation of the fluorescent derivative precedes the decarboxylation. For the Bacillus stearothermophilus enzyme the formation of the fluorescent NAD derivative is an all-sites reaction and is accompanied by the removal of 4 CO_2 molecules showing conclusively that CO_2 has come from the subunits carrying the fluorophore.It is known that the yeast enzyme can be carboxymethylated either at 4, or under carefully controlled conditions, at 2 of the active site SH groups. Experiments with ~(14)C-labelled NAD~ show that both the tetrakis and his carboxymethylated enzymes form 2 molecules of the fluorescent NAD derivative. However, for the biscarboxymethylated enzyme, only on     

周期性负载变化提高乙醇燃料电池效率(英文)

We present a simple method to increase the efficiency of a direct ethanol fuel cell by a periodic modulation of the load(pulsed mode). The fuel cell was periodically short circuited with a resistor(1 Ω) for a few seconds(high load period) followed by a low load period of up to 100 s when the resistor was disconnected. The open circuit voltage(OCV) values before and after the short circuit of the cell showed an increase of up to 70 mV. The higher OCV was due to the oxidation and removal of strongly adsorbed CO during the electric short circuit when the electric potential of the anode was increased to be close to the cathode potential. The depoisoned anode surface was much more active directly after the short circuit. The slow decrease of the OCV observed after the short circuit was caused by the subsequent poisoning of the anode surface, which can be neutralized by another short circuit. In general, a stable increase in cell performance was obtained by repetition of the electric short circuit. The data showed that the pulse mode gave an increase in the power generated by the direct ethanol fuel cell by up to 51% and was 6% on average. It is anticipated that this mode of operation can be used also in different types of polymer electrolyte membrane fuel cells where CO poisoning is a problem, and after optimization of the parameters, a much higher gain in efficien-cy can be obtained.     

SOLVENT EXTRACTION OF VANADIUM (Ⅴ) FROM AQUEOUS SOLUTIONS BY PRIMARY AMINES

Vanadium (Ⅴ) can be quantitatively extracted by primary amines from nearly neutralchromium (Ⅵ) containing aqueous solutions Under similar conditions wtth equilibriumaqueous phase pH above 7, no vanadium can practically be extracted by tertiary amines whileextraction by secondary amines is only about 25--30%. The quantitative extraction of vana-dium from aqueous solutions containing no chromium (Ⅵ) can be obtained by adding acidto the extent that the ratio of gram equivalents of H~ added to the gram atoms of vanadiumin the apueous solution is equal to one or slightly higher. The mechanism of axtraction isbelieved to be solvation with molecular association between primary amines and tetravanadicacids through hydrogen bonding.