Calcium-activated proteolytic activity in rat liver mitochondria |
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Authors: | David G. Beer Jerry J. Hjelle Dennis R. Petersen Alvin M. Malkinson |
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Affiliation: | 1. School of Pharmacy, University of Colorado, Boulder, Colorado, USA, 80309;2. Clinical Pharmacology-Toxicology Center, College of Health Sciences and Hospital, 59th and Rainbow Boulevard, Kansas City, Kansas, USA, 66103 |
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Abstract: | Soluble extracts from sonicated rat liver mitochondria and rat liver cytosol were each chromatographed on DEAE-cellulose columns, and the fractions assayed for Ca2+-activated proteolytic activity using 14C-casein as a substrate. The mitochondrial preparations were shown to be free of cytosolic and microsomal contamination by the lack of alcohol dehydrogenase activity, a cytosolic marker enzyme, and by a lack of cytochrome P-450 activity, a microsomal marker enzyme. Two peaks of Ca2+-activated neutral endoprotease activity were resolved from the mitochondrial fractions. One protease was half-maximally activated with 25 μM Ca2+, and the other by 750 μM Ca2+. Rat liver cytosol contained only a high Ca2+-requiring protease peak. This is the first demonstration of Ca2+-activated proteases in mitochondria. |
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