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Biomedical subjects

T V Venkstern

Publications and source records attributed to T V Venkstern.

18 recordsLinked to original sources
PubMed1979

Primary structure of the nucleic acid from the 1,4-alpha-glucan branching enzyme.

The primary structure of the nucleic acid from the branching enzyme 1,4-alpha-D-glucan: 1,4-alpha-D-glucan 6-alpha-(1,4-alpha-glucano)-transferase (2.5-S RNA) isolated from rabbit muscles has been elucidated. The polyribonucleotide consists of 31 nucleotides; the unique features of the polyribonucleotide are the unusually high content of modified nucleotides (32%) and guanine residues (40%). Apparently 2.5-S RNA belongs to a class of nucleic acids unknown up to now. It is the first time that the structure of a nucleic acid component from a ribonucleoenzyme has been defined. This work is a preprequisite for gaining insight into the intimate activating effect of the poly-ribonucleotide on the enzyme action.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1979

The mechanism of action of tRNA methylases studied with immobilized tRNAs.

Each of the individual tRNAs immobilized on aminohydroxybutyl-cellulose (ABC) through their oxidized 3'-terminal binds affinitively all methylases present in the enzyme extract irrespective of whether this tRNA will be involved in the following step of methylation or not. These data allow to suggest that (a) the formation of a methylase-tRNA complex and the catalytic act of methylation are indeed autonomous processes and (b) the first step of interaction between tRNAs and tRNA methylases is rather unspecific and consists in the recognition of the whole class of tRNA molecules.

Animals↗
PubMed1977

Complementary addressed modification of yeast tRNA Val 1 with alkylating derivative of d(pC-G)-A. The positions of the alkylated nucleotides and the course of the alkylation in the complex.

Yeast tRNA Val 1 alkylation with 2', 3'-O-4-(N-2-chloroethyl-N-methylamino) benzylidene d(pC-G)-A proceeds at 20 degrees - 30 degrees C in the complementary complexes which are formed by d(pC-G)-A greater than RC1 binding to 3 sequences of tRNA Val 1 : psi-C-G58 in the T loop, C-G40 at the 3'-side of the anticodon loop and C-G18 in the D loop. The reaction in the complexes results in A53, I35, and psi 13 alkylation to form beta-/N-methyl-N-(formylphenyl 17 amino/ethyl-tRNA Val 1 with the relative rate constants of the alkylation that are 3 or 2 orders of magnitude higher than that for the alkylation without a complex formation. It is the third nucleotide from the 5'-terminus of the binding site of the modifying agent that is subjected to alkylation in the t RNA Val 1. The course of the alkylation does not depend on the possible base pairing of the 3'-terminal nucleotide of the reagent. The extent of the reagent binding and the relative rate constants of the alkalytion in the complexes indicate the following order of the complex stability: (psi-C-G58) greater than (CO-G40) approximately (C-G18) at 20 degrees and (psi-C-G58) greater than (C-G40) greater than (C-G18) at 30 degrees.

Alkylating Agents↗
PubMed1976

On the mechanism of tRNA methylase-tRNA recognition.

In order to further elucidate the mechanism of tRNA methylase-tRNA intreaction the methylation of some individual tRNAs separately and by pairs was performed. In conditions of tRNA excess the methylation rates of positionally analogous nucleotides in tRNA molecules are not summed up when two substrates are simultaneously present in the reaction mixture. The inhibitory action of yeast tRNASer, possessing m5c in position 29, on the methylation of C29 in other individual tRNAs was shown. Yeast tRNAVal which possesses an A residue in position 27 was shown to inhibit the methylation of G27 in E. coli tRNAMet. The data obtained confirm the suggestion that tRNA methylases recognizes the tertiary structure of tRNAs. They show also that the recognition and the proper catalytic action are two autonomous processes and that the former at least in its first stage is rather unspecific.

Animals↗
PubMed1976

[Estimation of kinetic constants and study of site specificity of Zajdela ascite hepatoma and rat liver tRNA-methylases].

Individual yeast tRNAVal1 was used as a substrate for estimation of kinetic constants and study of site specificity of m5C-and m1A-methylases of Zajdela ascite hepatoma and rat liver. It was demonstrated that the rate of yeast tRNAVal1 methylation by hepatoma tRNA-methylases is 4--5 times higher than that induced by liver tRNA-methylases. The rates of 1-hour methyl groups incorporation into tRNAVal1 were 3.7 and 4.7 times higher in case of m5C-and m1A-methylases and 9.4 and 4.5 times higher in case of m1G-and m7G-methylases of hepatoma than the respective rates obtained for corresponding liver methylases. The main products of methylation were m5C and m1A containing about 90% of total radioactivity incorporated into tRNA. m5C-methylases of liver and hepatoma had similar affinity for S-Ad-Met. The Km value for both enzymes was 2.66 micronmole; the Km values for m1A-methylases of liver and hepatoma with respect to S-Ad-Met were the same and equal to 0,25 micronmole. m5C and m1A methylases of liver and hepatoma had adequate affinity for yeast tRNAVal1; their site specificity was the same, since they methylated in yeast tRNAVal1 cytosine in the tetracytidylic sequence of C49--C52 and adenine in the 59th position from the 5'-end of the molecule.

Amino Acid Sequence↗
PubMedDate not supplied

[The existence of the ribonucleoprotein branching enzyme in rabbit skeletal muscle and ribozyme corresponding to it].

Amylose isomerase (AI) preparations were isolated from rabbit muscles after Petrova et al., as well as by the additional fractionation steps. Their homogeneity, enzymatic activity and RNA, isolated from those preparations, were characterized. AI preparations, as described by Petrova et al., proved to be heterogeneous in respect to the protein and RNA; by using additional fractionation methods RNA and protein have been separated from each other, which proves that a homogeneous stable ribonucleoprotein complex, exerting AI activity, does not exist. It was shown by three independent methods that AI preparations isolated after Petrova do not display branching, but have amylolytic activity. RNA, isolated along with the AI preparations, proved to be mainly total tRNA degraded to different degrees. No RNA corresponding to the previously sequenced 2.5S RNA could be detected in these preparations. RNA preparations do not manifest neither branching, nor amylolytic activity. Our data prove that there is no ribozyme, whose existence has been suggested previously.

1,4-alpha-Glucan Branching Enzyme↗
PubMedDate not supplied

[tRNA-methylase study of the extreme thermophile, Thermus flavus].

tRNA methylases were studied in the extreme thermophilic culture of Thermus flavus, strain 71. Like E. coli, the culture contained only those tRNA methylases which catalysed the formation of m1A and m7G. Mg2+, Ca2+ and Na+ ions activated tRNA methylases of Thermus flavus in the series Mg greater than Ca greater than Na while Mn2+ ions inhibited the enzyme. The activity of tRNA methylases was higher in T. flavus than in E. coli, and required less protein and time for exhaustive methylation of tRNA preparations. The overall activity of methylases in T. flavus at 70 degrees C was 5-6 times higher than at 40 degrees C; the elevation of temperature had different effect on various methylases: the activity of m1A methylase increased 13-fold whereas that of m7G methylase only twofold.

Chemical Phenomena↗
PubMedDate not supplied

[Comparative study of the tRNA-methylases of normal and tumor tissues. I. Spectrum of renal and carcinoma RA methylases].

A comparative study of rat kidney and carcinoma RA tRNA-methylase activity has been carried out using partially purified enzyme preparations and total E. coli tRNA. Also the nuclease activity of the methylase preparations from kidney and carcinoma was compared. It was established that the methylase activity in carcinoma preparations is higher, whereas the nuclease activity is lower in comparison to the enzyme preparations from liver. No formation of some specific methylated compounds could be established in the case of carcinoma. It was established that the relative contribution of individual methylases to the elevated level of total tRNA-methylase activity in carcinoma is different. Maximal enhancement of activity was established for the methylase forming m5U, whereas the activity of the enzymes, transfering the methyl group to the fifth position of C is practically equal in kidney and carcinoma tissues. Experimental results and theoretical evaluation of the hypotheses suggested to explain the higher methylase activity in tumor tissues allowed to reject some of them.

Animals↗
PubMedDate not supplied

[Comparative study of the tRNA-methylases of normal and tumor tissues. II. Positional specificity of renal and carcinoma RA methylases].

A comparative study of the position specificity of tRNA-methylases from normal and tumour tissues was performed on yeast tRNA1Val as the substrates using partially purified enzyme preparations from rat kidney and carcinoma RA. As in the case of rat liver and Novikoff hepatoma, two methylated compounds are formed in yeast tRNA1Val under the action of rat kidney and carcinoma enzyme preparations: m5C is formed in the sequence C49--C52 located in the extra loop and A59 in the Tpsi-loop is is converted into m1A. The activity of m5C-methylase [S-Ado-Met-tRNA-(cytosine-5)methyltransferase] (E. C. 2.1.1.29) is approximately equal in both tissues, whereas the activity of m1A-methylase [S-Ado-Met-tRNA-(adenine-1)methyltransferase] (E. C. 2.1.1.36) in carcinoma is twice as high as in the kidney. The two enzymes do not differ in their position specificity.

Animals↗
PubMedDate not supplied

[Amino oxyadsorbents. New type of adsorbents for affinity chromatography: purification of tRNA-methylases from rat nephron on aminooxybutylcellulose with immobilized tRNA].

A new type of sorbents for affinity chromatography is suggested and used to purify tRNA methylases. tRNA was immobilized on aminooxybutylcellulose via the oxidized 3'-end. In order to bind other enzymes specific for nucleic acids in general, e. g. nucleases, and to achieve a higher degree of purification the crude enzyme preparation was treated with rRNA immobilized on aminooxybutycellulose. The sequential application of two sorbents mentioned allows to get an approximately two hundred fold purification of total tRNA methylases. In a separate experiment the possibility of individual tRNA methylase fractionation by means of elution with a NACl gradient was shown; the degree of purification for some methylases was more than a thousand fold.

Animals↗
PubMedDate not supplied

[Nucleotide composition and digestion by nucleases of RNA from muscle amylose isomerase].

The primary structure of homogeneous low molecular RNA preparation with the sedimentation coefficient 2.5S isolated from amilose isomerase (A1) of muscle (E.C. 2.4.1.18) was analysed. This RNA can be digested by venom phosphodiesterase as well as by pancreatic and T2 RNAases; hence we conclude that the polynucleotide chain of A1 RNA consists of 3.5-phosphodiester bonds common for all RNAs. The nucleotide composition of the RNA was studied by two-dimensional TLC followed by spectrophotometry. The results show that its chain is 31--32 nucleotides long. High content of unusual components (about 30%) and guanine (about 40%) are specific features of this RNA.

1,4-alpha-Glucan Branching Enzyme↗
PubMedDate not supplied

[Inhibiting effect of S-adenosyl-L-homocysteine and its structural analogs on the process of enzymatic methylation of tRNA].

The action of S-adenosyl-l-homocysteine (S-Ado-Hcy), its four structural analogues S-Ino-Hcy, S-Guo-Hcy, S-Urd-Hcy, S-Cyd-Hcy and the five corresponding sulfoxides on tRNA methylases has been investigated. The data obtained in the study of overall incorporation of 14CH3-groups into an unfractioned tRNA preparation suggested that both the affinity of the inhibitors tested for various methylases and the type of inhibition were different. The experiments performed with unfractioned tRNA preparation permit to get an idea of the average inhibitory potency of each of the compounds. The study of their action on individual tRNA methylases by means of fractionation of minor components produced demonstrated that the affinity of the inhibitors tested for various methylases was really different. Thus, S-Ado-Hcy, S-Ino-Hcy and S-Urd-Hcy practically do not inhibit m1A methylase but have the highest affinity for m5C methylase. In an experiment with tRNAPhe which is a substrate for a single, namely m5C methylase, the type of inhibition of this methylase by S-Cyd-Hcy was revealed; it was found to be non-competitive with respect to S-Ado-Met, and the S-Cyd-Hcy concentration reducing the methylation by 50 percent was 1.2-10(-4) M.

Actinomycetales↗
PubMedDate not supplied

Use of the method of mixed substrates to study the specificity of tRNA methylases.

The absence of summation of the rate of methylation of positionally analogous cytidine residues in tRNA1Val, tRNAPhe, and tRNAMet in the case of simultaneous presence of two substrates in the incubation mixture was demonstrated by the method of mixed substrates. The same result was also obtained in the methylation of A19 (counting from the 3' end of the molecule) in tRNA1Val, tRNAPhe, tRNAfMet, tRNASer, and tRNAGlu individually and in the case of their mixing in pairs. These data are evidence that positionally analogous nucleotides in different RNAs are attacked by the same enzyme. Yeast tRNASer, already possessing a methyl group at the cytidine residue studied, proved to be an effective inhibitor of methylase, forming m5C with valine and phenylalanine tRNAs. The results obtained are evidence that differences in the primary and secondary structures at the site of methylation are not the deciding factors in the interaction of tRNA with methylases.

Base Sequence↗