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Query: UNIPROT:P06889 (Mol)
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Adenosine aminohydrolase from calf intestinal mucosa is sensitive to changes in its environment produced by small mole fractions of dimethylsulfoxide (DMSO). At a mole fraction of 0.1 where the dielectric constant is lowered from that of 78 of neat water to about 76.5, Vmax was reduced by 65% and affinity for substrate (adenosine) and the two competitive inhibitors, insine and N6-benzyladenosine, was decreased markedly. However, this decreased affinity was such that Ki/Km remained virtually constant for both inhibitors. DMSO itself showed the kinetics of a mixed inhibitor with Ki decreasing with increasing mole fraction. This cosolvent also decreased the heat stability of the enzyme which suggests that enzyme conformation is altered by DMSO. Comparison of data in the presence of DMSO with previously obtained data with dioxane shows that heat stability as well as Vmax, at a given value of dielectric constant, is independent of the amount or nature of cosolvent used to achieve that dielectric constant. However, cosolvent induced changes in Ki indicate that colligative as well as dielectric constant effects contribute to the observed changes in kinetic behavior. These experiments may be considered as models for the behavior of enzymes in the medium of lowered dielectric constant expected in the vicinity of cytoplasmic membranes. The results indicate that in such an environment, adenosine aminohydrolase would be expected to be less efficient a catalyst, but equally susceptible to product inhibition, as compared to media of dielectric constant approaching that of water.
Mol Cell Biochem 1976 Aug 30
PMID:Cosolvent-buffer mixtures as models for the cytoplasmic mileu: the enzymology of adenosine aminohydrolase. 98 42

On the basis of published measurements of the melting transitions of synthetic polydeoxyribonucleotides with known sequences we have determined the parameters of the interplane (stacking) interactions of base pairs in DNA over the range of ionic strengths from 0.01 to 0.1 M Na+. We found that deviations of the stacking-interaction energy from the mean value of 7-8 kcal/mole were extremely small and did not exceed 0.2 kcal/mole. We report an analysis of the influence of the heterogeneity of the stacking interactions on the melting parameters of polynucleotides with random sequences (models of natural DNA's). Inclusion of this effect does not significantly distort the linear dependence of the melting temperature on the relative content of G-C pairs and insignificantly affects the width of the helix-coil transition in DNA under normal conditions. However it is the heterogeneity of the stacking interactions that plays the crucial role in the melting of DNA under conditions where the difference between the relative stabilities of the A-T and G-C pairs tends to zero, as in concentrated solutions of tetraethylammonium and tetramethylammonium salts.
Mol Biol (Mosk)
PMID:Influence of base sequence on the stability of the double helix of DNA. 102 45

The nucleotide composition, relative concentration of pyrimidine clusters, and the degree of methylation of the mitochondrial and nuclear DNA's of various vertebrates and the protozoan Crithidia oncopelti have been studied. With respect to the relative concentration of GC pairs, the mtDNA of animals (bull, rat) does not differ from the corresponding nDNA. The relative concentration of GC pairs in the mtDNA of certain fish and birds is 1.5-2.5 mole% higher than in the respective nDNA. The kinetoplast DNA of the protozoan C. oncopelti (where the relative concentration of the GC pairs is 42.9 mole %) differs very sharply in composition from the nDNA (where the relative concentration of GC pairs is 51.3 mole %). The mtDNA's and kDNA's studied are distinguished from the respective nDNA'S by a lower degree of clustering of pyrimidine nucleotides. The proportion of mono- and dipyrimidine fragments in the mtDNA and kDNA is 30 mole %, while in the nDNA it does not exceed 23 mole %. The relative concentration of long pyrimidine clusters (hexapyrimidine clusters of larger) in the mtDNA is smaller than in the nDNA by a factor of 2-5. The low degree of clustering of the pyrimidine nucleotides is apparently characteristic of all the known mtDNA's and may support the fact that they have a single type of organization and are of a single origin. All the vertebrate mtDNA's studied contain 5-methylcytosine as a minor base (1.5-3.15 mole %), and their level of methylation is 1.5-2 times greater than that in the respective nDNA's. It has been shown that animals display species specificity with respect to the 5-methylcytosine content in the mtDNA. Its distribution among the pyrimidine clusters in the bovine heart mtDNA differs substantially from that in the nDNA. This suggests that the methylation specificities of nuclear and mitochondrial DNA are different. A DNA methylase, which effects the in vitro methylation of cytosine residues both in the homologous mtDNA and in different heterologous DNA's, has been found in rat liver and bovine heart mitochondria. The specificity of the in vitro methylation of the cytosine residues in the same heterologous Escherichia coli B DNA by the nuclear and mitochondrial enzymes is different: The mitochondrial enzyme methylates predominantly in monopyrimidine fragments, and the nuclear enzyme methylates mostly in di- and tripyrimidine fragments. They, therefore, recognize different nucleotide sequences.
Mol Biol (Mosk)
PMID:Structure of animal mitochondrial DNA: nucleotide composition, pyrimidine clusters, and methylation character. 102 50

The reaction of O-beta-diethylaminoethylhydroxylamine (O-beta-HA) with cytidine was studied and its mechanism was shown to be analogous to that of the reaction of hydroxylamine of O-methylhydroxylamine with cytidine. In experiments involving reaction of denatured DNA with O-beta-HA., Sephadex G-15 columns were used for the quantitative separation of normal and modified nucleosides after enzymatic hydrolysis of modified DNA by exonuclease A5 followed by alkaline phosphatase treatment. DNA cytidine residues of free cytidine with O-beta-HA. Modified cytidines can form complex with phosphotungstic acid (PTA). It was shown that one mole of PTA was bound per one mole of modified cytidine either in DNA or in free state. Electron microscopic examination of denatured DNA molecules modified by O-beta-HA and reacted with PTA revealed linear arrays of electron-scattering spots which presumably correspond to PTA molecules complexed with modified cytidine in DNA chains.
Mol Biol (Mosk)
PMID:[Double modification of cytidine residues in DNA]. 105 81

Variation of ribonuclease S structure is analysed with the potential energy being minimized by a computer. The function of potential energy contains the potentials of bond and angle distortions, torsional and non-valent interactions. It is shown that after 100 iterations the potential energy is decreased from the value of 6500 kcal/mole to--1012 kcal/mole, 92% of complete change of energy fitting the first ten iterations. The root mean square deviation (r. ms. d.) of final structure from the initial one is 0.232 A (0.206 A for the backbone and 0.257 A for side groups). The forbidden non-valent contacts are completely removed after minimization. R. ms. d. of the equilibrium value is decreased from 0.097 to 0.006 A for bond lengths; from 7.660 to 3.65 degrees for valence an-les and from 9.44 to 6.95 degrees for rotation angles around the peptide bonds. Distribution of tensions along the protein chain after minimization is considerably changed, the tensions decreasing in average by 100 times.
Mol Biol (Mosk)
PMID:[Theoretic analysis of conformation of proteins. I. Minimization of potential energy of ribonuclease S]. 105 89

Germination of wheat seeds results in small changes of the GC content of total DNA (from 47.5 to 49.0 mole %): at the same time the amount of 5-methylcytosine in seeds 10 hours after wetting and at day 3 of germination significantly decrease (from 6.0 to 5.4 and 5.2 mole %, respectively). The wheat genome is methylated in non-uniform fashion: moderute repeats (less than a hundred copies, interval Cot = 0,12 . 10(2)-420) possess the maximal amount of 5-methylcytosine, while the unique sequences (Cot greater than 420) have the lowest 5-methylcytosine content. Methylation of highly reiterated sequences (Cot less than 0,8 . 10(-2) is similar to that of the total DNA. At day 3 of germination the amount of 5-methycytosine in all DNA fractions is lower as compared with these fractions isolated from DNA of dormant seeds. This is probably due to (1) diminution in the amount of reiterated sequences with high 5-methylcytosine content and (2) to lowering of DNA methylation level in germinating seeds. Changes in DNA methylation may be associated with the regulation of gene activity in the differentiating plant cells at various stages of ontogenesis.
Mol Biol (Mosk)
PMID:[Changes in base composition and molecular population of wheat DNA on germination]. 105 92

50-S ribosomal subunits from the extreme halophilic bacterium, Halobacterium cutirubrum, contain an alanine-rich acidic "A" protein which resembles the L7--L12 multimer (Kaltschmidt and Wittmann, 1970) found in the 50-S ribosomal subunit of Escherichia coli cells. The protein contains 24 mole % alanine and is devoid of histidine, tryptophan and cysteine. Unlike E. coli which has two forms of the "A" protein distinguished solely by the acetylation state of the serine amino terminus. H. cutirubrum 50-S subunits contain only one unsubstituted form of the "A" protein in vivo. However, during purification of ribosomes from cells grown between 25 and 37 degrees C the latter "A" protein undergoes rapid, specific, in vitro enzymatic alteration at its carboxy-terminal end. When the halophile is grown in the temperature range of 40 to 42 degrees C the cleaving enzyme is not active and only one form of the "A" protein is found on the ribosomes.
Mol Gen Genet 1975 Sep 15
PMID:Temperature related alterations in the acidic alanine-rich "A" protein from the 50S ribosomal particle of the extreme halophile, Halobacterium cutirubrum. 110 49

The interaction of the oligonucleotides ApApA, ApApU and ApApC with polyribouridylic acid and of hexariboinosinic acid with and without phosphate near the 3'-end with polyribocytidylic acid was studied by the method of equilibrium gel filtration through Sephadexes. The free energy, the energy and entropy of the complexing were calculated from isotherms of the adsorption of the oligonucleotides on the polynucleotides in relation to the composition of the oligonucleotides and the concentration of magnesium ions in the buffer. It was shown that in the case of the interaction of ApApA and ApApC with poly(U) a perfect triple complex is formed, while in the case of the interaction of ApApU with poly(U) the noncomplementary base is partially displaced from the complex. The free energy of the interaction of neighboring oligonucleotides in a complex with polynucleotides is from --1000 to --3000 cal/mole depending on the type of the complex. It was shown that after the interaction of hexainosinic acid with poly(C) a double complex is formed. The free energy of the interaction of neighboring oligonucleotides in this complex is formed. The free energy of the interaction of neighboring oligonucleotides in this complex is about --1200 cal/mole. Magnesium ions have a different effect on the formation of triple and double complexes in the interaction of oligonucleotides with polynucleotides.
Mol Biol 1975 Jan
PMID:A study of the interaction of oligonucleotides with polynucleotides by the method of equilibrium gel filtration. The effect of magnesium ions and the composition of the oligonucleotides on the stability of the complex. 112 8

About 2% of mouse DNA reassociates at extremely low Cot values (10-7-10-6 mole-liter-1-sec). This DNA fraction was isolated with the aid of nuclease S1 and purified by chromatography on hydroxyapatite. The study of this fraction suggests that it has a structure of hairpin type. The DNA of the hairpins can hybridize with sequences forming the double-stranded regions in pre-mRNA. Probably at least some of the DNA of the hairpins, described as "reversed repeating sequences" of DNA, is transcribed with the formation of structures of hairpin type in pre-mRNA.
Mol Biol 1975 Jan
PMID:Structure of nuclear pre-mRNA. VI. "Reversed repeats" in animal DNA and their hybridization with double-stranded regions of pre-mRNA. 116 48

The 1 P+f phage, a virulent mutant of the moderate P+ phage for Bac. brevis var. G.-B., consists of a hexagonal head (90x90 nm) and a long non-contractile tail (340 nm). This phage is characterized by a relatively long latent period (90-110 min) and a low yield (40-50 particles per cell). The 1P+f phage is quite stable at pH values from 1 to 11, insensitive to osmotic shock, treatment with chloroform and acridine orange. The sensitivity of the phage to thermal treatment and UV-radiation has been studied. The nucleic acid of the P+f phage is double-stranded DNA of AT-type (GC equals 34.5 mole %) which contains 5-methylcytosine (0.18 mole %) and N6-methyladenine (0.32 mole%). The level of methylation of cytosine and adenine residues in DNA of the 1 P+f phage does not depend on the host studied (Bac. brevis, P- and S variants). The specificity of methylation of cytosine residues in the S and P- cells appears to be the same. DNA of the 1 P+f phage strongly differs from DNA of the host in nucleotide composition (GC equals 45.7 mole %). Nevertheless, phage DNA is very similar to DNA from Bac. subtilis in the character of pyrimidine distribution (the amount of different pyrimidine isopliths). This may testify to a somewhat common character of the nucleotide sequence organization in DNA of the phage and its host.
Mol Biol (Mosk)
PMID:[Some properties of 1 P+f bacteriophage for Bacillus brevis var. G.-B and its nucleic acid]. 121 2


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