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Cholesterol side chain cleavage in rat adrenal supported by outer mitochondrial membrane NADH-semidehydroascorbate
The Journal of Biological Chemistry
|April 10, 1985
Summary
Rat adrenal mitochondria possess a rotenone-insensitive outer membrane enzyme that aids cholesterol side chain cleavage. This finding offers new insights into the role of ascorbic acid in corticosteroidogenesis.
Area of Science:
- Biochemistry
- Mitochondrial Biology
- Steroidogenesis
Background:
- Rat adrenal mitochondria contain an outer membrane NADH-semidehydroascorbate (NADH-SDA) reductase.
- This enzyme is rotenone-insensitive and plays a role in cholesterol side chain cleavage.
Purpose of the Study:
- To investigate the function of outer mitochondrial membrane NADH-SDA reductase in rat adrenal mitochondria.
- To elucidate the role of this enzyme in supporting cholesterol side chain cleavage and corticosteroidogenesis.
Main Methods:
- Enzyme activity assays measuring cholesterol side chain cleavage.
- Inhibition studies using cycloheximide.
- Assessment of requirements for catalase or butylated hydroxyanisole.
- Mitochondrial preparation treatments at -20 degrees C.
Main Results:
- Outer mitochondrial membrane NADH-SDA reductase supports cholesterol side chain cleavage at a rate comparable to malate.
- Cycloheximide equally inhibits activity from both NADH-SDA reductase and malate.
- Catalase or butylated hydroxyanisole are necessary for NADH-SDA reductase-supported cleavage, but this requirement is abolished by cold treatment.
- Ascorbic acid alone or with malate shows inhibitory or no effect on side chain cleavage.
Conclusions:
- Outer mitochondrial membrane NADH-SDA reductase provides cytoplasmic reducing equivalents to intramitochondrial cytochrome P-450scc.
- This enzyme offers a novel explanation for ascorbic acid's function in corticosteroidogenesis.