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Electron transfer in chromaffin-vesicle ghosts containing peroxidase
G J Harnadek1, E A Ries, D G Tse
1Department of Biological Sciences, Wayne State University, Detroit, MI 48202.
Biochimica Et Biophysica Acta
|June 29, 1992
Summary
The ascorbate regeneration system in chromaffin vesicles, involving cytochrome b-561, can support various enzymes, not just dopamine beta-monooxygenase. This system facilitates electron transfer to semidehydroascorbate within vesicles.
Area of Science:
- Biochemistry
- Cell Biology
- Neuroscience
Background:
- Chromaffin vesicles contain dopamine beta-monooxygenase, converting dopamine to norepinephrine.
- Intravesicular ascorbic acid is thought to supply reducing equivalents, regenerated via cytochrome b-561 electron transport from the cytosol.
Purpose of the Study:
- To investigate if the ascorbate regeneration system supports enzymes beyond dopamine beta-monooxygenase.
- To determine the role of cytochrome b-561 in electron transfer to semidehydroascorbate.
Main Methods:
- Utilized chromaffin-vesicle ghosts loaded with ascorbic acid and exogenous horseradish peroxidase.
- Monitored the redox state of cytochrome b-561 in response to hydrogen peroxide addition.
Main Results:
- Cytochrome b-561 was reduced when both ascorbate and peroxidase were present internally.
- Addition of H2O2 caused partial oxidation of cytochrome b-561, indicating electron transfer to semidehydroascorbate.
- This oxidation was dependent on the presence of both internal ascorbate and peroxidase.
Conclusions:
- Cytochrome b-561 facilitates electron transfer to internally generated semidehydroascorbate.
- The ascorbate regeneration system is versatile and can support diverse ascorbate-utilizing enzymes within vesicles.