Related Experiment Videos
Formation and reduction of ascorbate radicals by hog thyroid microsomes
1Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan.
Archives of Biochemistry and Biophysics
|August 15, 1993
Summary
Thyroid microsomes generate ascorbate radicals, which are reduced by NADH. Ascorbate protects thyroid hormones from oxidative damage via the NADH-cytochrome b5 reductase system.
Area of Science:
- Biochemistry
- Thyroid Physiology
- Enzymology
Background:
- Thyroid microsomes play a role in thyroid hormone metabolism.
- Ascorbate (Vitamin C) is an antioxidant.
- NADH-cytochrome b5 reductase is an enzyme involved in electron transport.
Purpose of the Study:
- To investigate the role of ascorbate radicals in thyroid microsomes.
- To examine NADH-dependent electron transport in thyroid microsomes.
- To understand how ascorbate protects thyroid hormones from oxidative degradation.
Main Methods:
- Electron Spin Resonance (ESR) experiments to detect ascorbate radicals.
- Optical methods to monitor NADH oxidation.
- Enzyme kinetics to determine reductase activity.
Main Results:
- Ascorbate radical formation was observed in thyroid microsomes.
- NADH reduced ascorbate radicals, decreasing their steady-state concentration.
- Thyroxine stimulated ascorbate radical formation, which was inhibited by NADH.
- NADH-cytochrome b5 reductase in thyroid microsomes showed similar properties to liver microsomes.
Conclusions:
- Ascorbate radicals compete with cytochrome b5 for reduced NADH-cytochrome b5 reductase.
- Thyroid peroxidase initiates thyroxine-mediated ascorbate oxidation.
- Ascorbate, through the NADH-cytochrome b5 reductase system, protects thyroid hormones from oxidative breakdown.