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Linkage between proton binding and amidase activity in human gamma-thrombin
R De Cristofaro1, J W Fenton, E Di Cera
1Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110.
Biochemistry
|February 4, 1992
Summary
Human gamma-thrombin amidase activity shows pH-dependent Michaelis-Menten kinetics, with distinct protonation effects and salt concentration responses compared to alpha-thrombin. This study characterizes substrate binding and catalysis linkages.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Human gamma-thrombin is a protease with amidase activity.
- Understanding enzyme kinetics is crucial for drug development and biological process elucidation.
Purpose of the Study:
- To investigate the amidase activity of human gamma-thrombin across a pH range of 6-10.
- To analyze the influence of NaCl concentration and temperature on enzyme kinetics.
- To characterize the linkage between proton and substrate binding and its thermodynamic contributions.
Main Methods:
- Enzyme kinetics assays were performed.
- Michaelis-Menten parameters (Km and kcat) were determined.
- Thermodynamic analysis was employed to study binding and catalytic events.
Main Results:
- Km exhibited a bell-shaped pH dependence with a minimum around pH 7.9 (0.1 M NaCl, 25°C).
- kcat showed a bell-shaped pH dependence with a maximum around pH 8.6.
- Gamma-thrombin's response to NaCl concentration differed from alpha-thrombin, with reversed linkage observed at pH extremes.
Conclusions:
- Three groups influence gamma-thrombin amidase activity, with distinct pK values and perturbed enthalpies compared to alpha-thrombin.
- The study elucidates the complex interplay of pH, salt concentration, and thermodynamics in gamma-thrombin catalysis.