KINETIC STUDIES ON HUMAN CYSTEINYL‐t RNA SYNTHETASE
- 1 March 1979
- journal article
- research article
- Published by Wiley in International Journal of Peptide and Protein Research
- Vol. 13 (3) , 267-273
- https://doi.org/10.1111/j.1399-3011.1979.tb01878.x
Abstract
The detailed pH and temperature kinetics of human term placenta cysteinyl-tRNA synthetase (EC 6.1.1.16) were studied. The ATP-PPi exchange reaction catalyzed by the cysteinyl-tRNA synthetase was highly dependent on temperature, pH, and ionic strength. The Arrhenius plot at temperatures between 5° and 40° was linear, giving an activation energy of 19 ± 2.5 Kcal/mol. The pH dependence of the kinetic parameters Km and Vmax was investigated. Apparent pKa value of 6.4 was observed in the pH-dependence of Vmax/Km plot. The pH versus Vmax plot showed two apparent pKa values of about 5.8 and 7.8. Van't Hoff's enthalpies were used to differentiate the nature of the possible groups responsible for the ionization. These results are valuable for the selection of chemical modifying reagents in characterizing the amino acid residues involved in substrate (nucleotide) binding or catalysis.Keywords
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