Partial Purification of a Metalloprotease Catalyzing the Processing of Adrenodoxin Precursor in Bovine Adrenal Cortex Mitochondria

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Abstract
In vitro translation of bovine adrenal cortex RNA in rabbit reticulocyte lysate cell-free system produced the precursor form of adrenodoxin having a molecular weight of approximately 22,000 daltons, which was about 10,000 daltons larger than mature adrenodoxin. The precursor of adrenodoxin was efficiently imported into adrenal cortex mitochondria in vitro. The precursor was also imported into rat liver mitochondria, suggesting the lack of tissue specificity and species specificity of the import process. The enzyme which processed the precursor of adrenodoxin to the mature form was in the matrix fraction from bovine adrenal cortex mitochondria, and the processing protease was partially purified from the matrix fraction. The apparent molecular weight of the processing protease was about 60,000 daltons as determined by Sephadex G-150 gel filtration, and its activity was optimal at pH 8.5. The processing protease was not inhibited by various bacterial protease inhibitors examined. Metal chelators (EGTA, GTP, 8-hydroxyquinoline, and Zincon) inhibited the processing, and EDTA and o-phenanthroline were more strongly inhibitory than other chelators. The processing protease was completely inactivated by incubation with 10 μM EDTA, and its activity was restored by addition of excess amounts of Mn2+, Fe2+, or Co2+. These results indicate that the maturation of the precursor of adrenodoxin is catalyzed by a soluble metalloprotease in the matrix.