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Mechanism of inactivation of myeloperoxidase by propylthiouracil
1Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kobe-Gakuin University, Japan.
Abstract:
The mechanism of inactivation of myeloperoxidase purified from rat bone marrow by propylthiouracil (PTU) was studied. PTU inhibited not only the peroxidase activity but also the chlorinating activity of myeloperoxidase in a concentration dependent manner. When myeloperoxidase was treated with PTU and hydrogen peroxide (5 microM), inactivation of the enzyme was still observed after the excess reagents were removed by a column of Sephadex G-25. The treatment of the enzyme with PTU in the absence of hydrogen peroxide caused a slight inhibition of the enzyme activity. In addition, [14C]PTU became bound to myeloperoxidase in the presence of hydrogen peroxide. Difference spectrum of myeloperoxidase incubated with the small (0.1 mM) and large (2 mM) amounts of hydrogen peroxide revealed the formation of compounds II and III, respectively. Difference spectrum of myeloperoxidase treated with PTU in the presence of a low concentration of hydrogen peroxide (5 microM) was similar to that of compound II. Therefore, these results indicate that PTU inactivates myeloperoxidase through binding to the enzyme and the conversion to a compound II-like form in the presence of hydrogen peroxide.
Insights
Propylthiouracil (PTU) inactivates rat myeloperoxidase by binding to the enzyme. This inactivation occurs in the presence of hydrogen peroxide, forming a compound II-like structure.
Area of Science:
- Biochemistry
- Enzymology
- Pharmacology
Background:
- Myeloperoxidase (MPO) is a key enzyme in neutrophil function.
- Understanding MPO inactivation mechanisms is crucial for therapeutic development.
Purpose of the Study:
- To elucidate the mechanism by which propylthiouracil (PTU) inactivates purified rat myeloperoxidase (MPO).
Main Methods:
- Enzyme activity assays (peroxidase and chlorinating).
- Spectroscopic analysis (difference spectroscopy).
- Enzyme binding studies using radiolabeled PTU.
- Enzyme purification and gel filtration chromatography (Sephadex G-25).
Main Results:
- PTU inhibited both peroxidase and chlorinating activities of MPO in a dose-dependent manner.
- PTU-mediated inactivation persisted after reagent removal, indicating covalent modification.
- PTU binding to MPO was observed in the presence of hydrogen peroxide.
- Spectroscopic data suggested PTU induces a compound II-like state in MPO.
Conclusions:
- Propylthiouracil inactivates myeloperoxidase via binding to the enzyme.
- This inactivation is dependent on hydrogen peroxide and results in a compound II-like intermediate.
- The findings provide insight into the interaction of PTU with MPO.