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L L Kisselev

Publications and source records attributed to L L Kisselev.

23 records · Page 2Linked to original sources
PubMed1975

Limited proteolysis of the tryptophanyl-tRNA synthetase.

Earlier studies have shown that native tryptophanyl-tRNA synthetase from beef pancreas is composed of two apparently identical subunits having a molecular weight of 60000 plus or minus 2000 each. Incubation of the pruified enzyme with trypsin under restrictive conditions results in splitting of each subunit to form an enzymatically inactive polypeptide chain of mol. wt 24500 plus or minus 1500. During proteolysis, two distinct intermediate forms of mol. wt 51000 plus or minus 2000 and 40000 plus or minus 2000 and fragments of mol. wt 14000 plus or minus 2500 are formed. The presence of substrates, viz. ATP, tryptophan or tryptophanyl adenylate, decreases the rate of proteolysis. However, a band pattern monitored by acrylamide gel electrophoresis is qualitatively indistinguishable from that obtained in the absence of substrates. Native and trypsin-modified subunits (the latter having a molecular weight of 24500) have been maleylated, reduced, carbosymethylated and subjected to exhaustive digestion by trypsin followed by peptide mapping. Comparison of the finger prints has shown that the trypsin-modified subunit represents a polypeptide with lowered content of dicarboxylic amino acids. That the number of peptides revealed after complete proteolysis of native and trypsin-modified subunits does not favour the presence of long repetitive sequences in each subunit, is at variance with some bacterial aminoacyl-tRNA synthetases. Study of the fluorescence polarisation of 1-anilino-8-napthalene sulphonate adsorbed on the dimeric tryptophanyl-tRNA synthetase, indicates that the molecule behaves as a complete entity in Brownian rotation. The trypsin-resistant end products, composed of two types of polypeptides (mol. wts 24500 and 14000), remain associated with each other. From the mol. wt of this associate it follows that each fragment is present in the associate in duplicate. When the purification procedure was carried out in the absence of a protease inhibitor, the active modified enzyme form was obtained. As judged from the molecular weight values, it is composed of two equal subunits corresponding to one of the products of limited proteolysis. The data presented are compatible with compact three-dimensional structure of tryptophanyl-tRNA synthetase having very limited regions exposed to exogenous or endogenous proteolysis.

Adenosine Triphosphate↗
PubMed1975

A directed alteration of ribonuclease specificity. Hydrolysis of polyribonucleotides containing modified cytosine bases.

The action of ribonucleases on poly and oligoribonucleotides containing cytosine bases modified by methoxyamine and bisulphite was examined. Resistance of phosphodiester bonds in (Cp)nXp (where n greater than or equal to 1 and X stands for A, G or U) to T2 RNase hydrolysis was observed if substrates were modified chemically. The phenomenon formed the basis for isolation of (Cp)nXp blocks as an additional tool in sequence investigations. After modification of cytosine pancreatic RNase was unable to hydrolyse (Cp)nUp blocks. Therefore the specificity of pyrimidyl RNase may be narrowed to 'uridyl RNase'.

Cytosine↗
PubMed1975

Hybridization of pigeon globin messenger RNA with complementary DNA synthesized in vitro by reverse transcription: influence of the homopolymeric regions.

The kinetics of hybridization of pigeon globin messenger RNA with complementary cDNA synthesized by means of AMV reverse transcriptase is complex. Addition of poly A or poly U in excess to the reaction mixture normalized the kinetics. It is concluded that association of the complementary homopolymeric regions of mRNA and cDNA accelerates the complex formation between heteropolymeric sequences in a fraction of the molecules.

Adenine Nucleotides↗