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Relation between thyroid peroxidase, H2O2 generating system and NADPH-dependent reductase activities in thyroid
Molecular and Cellular Endocrinology
|July 1, 1985
Summary
Thyroid peroxidase and hydrogen peroxide (H2O2) generation involve distinct membrane orientations. This study clarifies the spatial separation of these components on the thyrocyte apical membrane for effective iodination.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Thyroid hormone synthesis requires iodination, occurring on the apical plasma membrane.
- This process depends on thyroid peroxidase and a hydrogen peroxide (H2O2) generating system.
- Understanding the localization of these components is crucial for thyroid function.
Purpose of the Study:
- To investigate the orientation of thyroid peroxidase and NADPH-dependent H2O2 generation within membrane vesicles.
- To determine the role of NADPH-NBT reductase activity in H2O2 production.
- To elucidate the spatial relationship between H2O2 generation and peroxidase activity.
Main Methods:
- Comparison of H2O2 generation, nitro blue tetrazolium (NBT) reductase activity, and peroxidase activity in membrane vesicles.
- Analysis of enzyme orientations relative to vesicle surfaces.
- Examination of NADPH-NBT reductase activity's contribution to H2O2 and superoxide (O-2) production.
Main Results:
- Thyroid peroxidase is oriented towards the luminal side of vesicles.
- The NADPH site for H2O2 generation is located on the external side.
- NADPH-NBT reductase activities on vesicle surfaces do not produce H2O2 or O-2.
Conclusions:
- Thyroid peroxidase and the NADPH site of H2O2 generation exhibit spatial separation on the apical membrane.
- A multi-component complex likely facilitates H2O2 generation.
- A model is proposed for the spatial arrangement of the H2O2 generation system and thyroid peroxidase.