1. 1. The activity of 3-β-hydroxysteroid dehydrogenase (3-β-hydroxysteroid: NAD (P) oxidoreductase, EC 188.8.131.52) in rat testis mitochondria and submitochondrial fractions was determined. 2. 2. Innr and outer mitochondrial membranes were obtained by subjecting the mitochondrial pellets to controlled osmostic lysis, ultrasonic vibration, and treatment with a non-ionic detergent, Lubrol WX, followed by differential centrifugation. 3. 3. The purity of the isolated mitochondria and of mitochondrial membranes was ascertained by electron microscopy, measurement of enzyme markers and by a method based upon labelling of the mitochondrial and cytoplasmic RNA with [5-3H]orotic acid. 4. 4. The results of this study suggest that the 3-β-hydroxysteroid dehydrogenase is present in rat testis mitochondria, free of endoplasmic reticulum and that this enzyme is mainly localized in the inner mitochondrial membrane.
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This work was supported by the Ford Foundation Grant No. to thank Mrs Miriam Kaufman for her skilled technical assistance.