[Role of the anticodon loop in triggering conformational changes of tryptophanyl-tRNA synthetase by tRNA Trp]. / Rol' antikodonovoi petli v induktsii konformatsionnykh izmenenii triptofanil-tRNK-sintetazy pod desitviem tRNKtrp.

The circular dichroic spectrum of the bovine tRNATrp is altered in complex with homologous tryptophanyl-tRNA synthetase showing the conformational changes of the substrate under the action of enzyme. The conversion of the exposed cytosine into uridine bases in tRNATrp (beef, yeast) does not prevent complex formation but abolishes the tRNA action on the limited proteolysis of the synthetase. It was shown that elimination of this type of tRNA activity is solely attributed to the cytosine leads to uridine conversion in the anticodon loop. A conclusion is made that the anticodon loop of the tRNATrp plays a dominant role in triggering conformational changes of the synthetase under substrate action whereas the CCA-end is not directly involved in this process.

[Immunochemical properties of tryptophanyl-tRNA synthetase and its fragments]. / Immunokhimicheskie svoistva triptofanil-tRNK-sintetazy i ee fragmentov.

The interaction between beef pancreas tryptophanyl-tRNA synthetase and its fragments produced after limited proteolysis, with IgG fraction of antiserum and with Fab fragment of IgG has been studied. Both the intact antibodies and Fab fragments inhibit the enzyme activity in tRNA aminoacylation and tryptophan dependent ATP-32P pyrophosphate exchange reactions. However, the enzyme inhibited by antibodies is still able to form a complex with tryptophanyl-tRNA. The enzymatically active fragment obtained after endogenous proteolysis interacts only with 1/3 of the antibodies against native enzyme. The fragment produced by trypsinolysis possess similar immunochemical properties. This fragment has almost the same molecular weight but is enzymatically inactive. Pure antibodies against tryptic fragment isolated by means of specific immunoabsorbent inhibit the enzymatic activity. The antibodies which do not interact with this fragment (2/3 of the total amount of antibodies) have no influence on the enzymatic activity. The immunochemical identity of the two synthetase fragments differing in their enzymatic activity supports the assumption that the loss of enzymatic activity of the tryptis fragment is caused by lack of a small peptide which is retained in case of endogenous proteolysis. Probably the amino acid residues of this peptide participate in formation of the active centre of tryptophanyl-tRNA synthetase. A new procedure for determination of the number of antigenic determinants in proteins is developed. It is shown by this method that beef pancreas tryptophanyl-tRNA synthetase contains 9 +/- 1 antigenic determinants.

[Immunochemical comparison of tryptophanyl-tRNA-synthetases]. / Immunokhimicheskoe sravnenie triptofanil-tRNK-sintetaz.

A fraction of immunoglobulins was isolated from the sera of rabbit immunised by a homogeneous beef pancreas tryptophanyl-tRNA-synthetase (TRSase). The IgG fraction was shown to inhibit the enzymatic activity during aminoacylation of yeast tRNATrp and tryptophan activation. By using the radioimmunoadsorption technique, the interaction of IgG was tested with TRSaes from beef pancreas and identical enzymes from other sources (contained in the total preparation). Beef liver TRSase efficiently inhibited the radioimmunoadsorption reaction of beef pancrease 125J-TRSase that suggests a strong similarity or even identity of the enzymes. When the purified antibodies to beef pancreas TRSase were isolated common antigen determinants were revealed for TRSase from beef pancreas, liver of chick, pig and rat. Enzymatic activity of TRSase from liver of beef, pig and chick was shown to be inhibited by antibodies to beef pancreas. TRSase whereas the enzymes from rat liver and yeast did not change their activity in the presence of these antibodies. Therefore, for several TRAases common antigen determinants have been revealed that suggest the presence of common structural elements in these enzymes; antibody binding inhibits the activity of some TRSases and does not affect that of others.

[Modification of tRNA 1 Val from yeast with monoperphthalic acid]. / Modifikatsiia drozhzhevoi tRNA 1 Val monoperftalevoi kislotoi

A method is proposed for analysis of natural and chemically modified polynucleotides which consists in enzymatic conversion of the polymer or oligomer into nucleosides followed by cation-exchange chromotography on the microcolumns. By using the method developed it was shown that after treatment of the yeast tRNAVal and tRNAPhe with monoperphthalic acid N-oxides of adenosine and cytidine were formed. Poly (U, G) was not modified at a measurable extent whereas GMP was decomposed. In tRNAVal (yeast)the adenosines and cytosines of the anticodon loop and 3'-end are most reactive; it is the case for the C17 of the diHU-loop as well. These data are in agreement with the results obtained for tRNA modification with other reagents and for limited enzymatic hydrolysis of the tRNAVal. The limitations of the reaction of the monoperphthalate with nucleic acids are briefly discussed.