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Ca2+ regulation of thyroid NADPH-dependent H2O2 generation
1Unité 96, INSERM, Unité de Recherche sur la Glande Thyroide et la Régulation Hormonale, Le Kremlin-Bicêtre, France.
FEBS Letters
|June 6, 1988
Summary
Calcium (Ca2+) activates a hydrogen peroxide (H2O2)-generating enzyme in thyroid tissue. This activation is reversibly modulated by calcium-releasable inhibitor proteins, suggesting a novel regulatory mechanism in thyroid function.
Area of Science:
- Biochemistry
- Endocrinology
- Cell Biology
Background:
- Thyroid particulate fractions contain an enzyme generating hydrogen peroxide (H2O2) dependent on NADPH.
- This enzyme's activity is known to be influenced by calcium ions (Ca2+).
Purpose of the Study:
- To investigate the mechanism of Ca2+ regulation of NADPH-dependent H2O2 generation in porcine thyroid tissue.
- To identify factors modulating the enzyme's Ca2+ sensitivity.
Main Methods:
- Solubilization and partial purification of the enzyme using CHAPS and DEAE chromatography.
- Preincubation of particulate fractions with Ca2+ to assess desensitization.
- Analysis of inhibitory effects of non-particulate fractions in the presence of EGTA.
Main Results:
- A partially purified enzyme extract lost Ca2+ dependence.
- Preincubation with Ca2+ rendered the particulate fraction Ca2+-insensitive.
- A non-particulate fraction inhibited the Ca2+-desensitized enzyme and the purified enzyme.
Conclusions:
- Reversible Ca2+ activation of NADPH-dependent H2O2 generation in porcine thyroid is modulated by calcium-releasable inhibitor proteins.
- These findings suggest a novel regulatory mechanism for thyroid enzyme activity involving inhibitory proteins.