Kinetic studies on human cysteinyl-tRNA synthetase

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Human term placenta cysteinyl-tRNA synthetase (EC 6.1.1.16) plays a vital role in protein synthesis.
• Enzyme kinetics provide critical insights into catalytic mechanisms and substrate interactions.

Purpose of the Study:

• To elucidate the detailed pH and temperature kinetics of human term placenta cysteinyl-tRNA synthetase.
• To investigate the influence of pH, temperature, and ionic strength on the enzyme's ATP-PPi exchange reaction.

Main Methods:

• Kinetic analysis of the ATP-PPi exchange reaction catalyzed by cysteinyl-tRNA synthetase.
• Determination of activation energy using Arrhenius plots.
• Investigation of pH dependence on kinetic parameters (Km and Vmax).
• Application of Van't Hoff's enthalpies to analyze ionization states.

Main Results:

• The enzyme's activity showed high dependence on temperature, pH, and ionic strength.
• An activation energy of 19 +/- 2.5 Kcal/mol was determined between 5 and 40 degrees Celsius.
• Apparent pKa values of 6.4 (for Vmax/Km) and approximately 5.8 and 7.8 (for Vmax) were identified, indicating specific ionization states affecting catalysis.

Conclusions:

• The kinetic parameters of cysteinyl-tRNA synthetase are significantly influenced by environmental factors like pH and temperature.
• The identified pKa values suggest the involvement of specific amino acid residues in the enzyme's catalytic mechanism and substrate binding.
• These findings are valuable for selecting chemical modifying reagents to further characterize the enzyme's active site.