Calcium-activated proteolytic activity in rat liver mitochondria
Beer, D.G.; Hjelle, J.J.; Petersen, D.R.; Malkinson, A.M.
Biochemical and Biophysical Research Communications 109(4): 1276-1283
1982
ISSN/ISBN: 0006-291X PMID: 6762879 Document Number: 188654
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 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 .mu.M Ca2+ and the other by 750 .mu.M Ca2+. Rat liver cytosol contained only a high Ca2+-requiring protease peak. This is the 1st demonstration of Ca2+-activated proteases in mitochondria.