Catalytic mechanism of isoleucyl-tRNA synthetase of Escherichia coli K10. Effect of pH and chemical modification

Biochemistry ◽  
1980 ◽  
Vol 19 (23) ◽  
pp. 5403-5411 ◽  
Author(s):  
Eggehard Holler ◽  
Gudrun Schwarze ◽  
Renate Scheibl ◽  
Beate Hammer-Raber
Keyword(s):  
Escherichia Coli ◽  
Chemical Modification ◽  
Catalytic Mechanism ◽  
Trna Synthetase ◽  
Effect Of Ph

scholarly journals Studies on chemical modification of thionucleosides in the transfer ribonucleic acid of Escherichia coli

1974 ◽  
Vol 143 (2) ◽  
pp. 285-294 ◽  
Author(s):  
Yarlagadda S. Prasada Rao ◽  
Joseph D. Cherayil
Keyword(s):  
Escherichia Coli ◽  
Amino Acids ◽  
Chemical Modification ◽  
Gel Filtration ◽  
Trna Synthetase ◽  
Aminoacyl Trna Synthetase ◽  
E Coli ◽  
Chemical Reagents ◽  
Mild Conditions ◽  
Trna Species

35S-labelled tRNA from Escherichia coli was treated with chemical reagents such as CNBr, H2O2, NH2OH, I2, HNO2, KMnO4 and NaIO4, under mild conditions where the four major bases were not affected. Gel filtration of the treated tRNA showed desulphurization to various extents, depending on the nature of the reagent. The treated samples after conversion into nucleosides were chromatographed on a phosphocellulose column. NH2OH, I2 and NaIO4 reacted with all the four thionucleosides of E. coli tRNA, 4-thiouridine (s4U), 5-methylaminomethyl-2-thiouridine (mnm5s2U), 2-thiocytidine (s2C) and 2-methylthio-N6-isopentenyladenosine (ms2i6A), to various extents. CNBr, HNO2 and NaHSO3 reacted with s4U, mnm5s2U and s2C, but not with ms2i6A. KMnO4 and H2O2 were also found to react extensively with thionucleosides in tRNA. Iodine oxidation of 35S-labelled tRNA showed that only 6% of the sulphur was involved in disulphide formation. Desulphurization of E. coli tRNA with CNBr resulted in marked loss of acceptor activities for glutamic acid, glutamine and lysine. Acceptor activities for alanine, arginine, glycine, isoleucine, methionine, phenylalanine, serine, tyrosine and valine were also affected, but to a lesser extent. Five other amino acids tested were almost unaffected. These results indicate the fate of thionucleosides in tRNA when subjected to various chemical reactions and the involvement of sulphur in aminoacyl-tRNA synthetase recognition of some tRNA species of E. coli.

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