title: A novel ATP-requiring protease from skeletal muscle that hydrolyzes non-ubiquitinated proteins.
abstract: Previously, we isolated an ATP-dependent proteolytic pathway in muscle, liver, and reticulocytes that requires ubiquitin and the enzymes which conjugate ubiquitin to proteins. We report here that skeletal muscle contains another soluble alkaline energy-dependent (but ubiquitin-independent) proteolytic activity. The cleavage of non-ubiquitinated protein substrates by the partially purified protease requires ATP hydrolysis since ATP in the absence of Mg2+, nonhydrolyzable ATP analogs, and pyrophosphate all fail to stimulate proteolysis. Proteolytic activity is also stimulated by UTP, CTP, and GTP, although not as effectively as by ATP (Km(ATP) = 0.027 mM). The enzyme is inactivated by the serine protease inhibitors diisopropyl fluorophosphate and 3,4-dichloroisocoumarin, but not by specific inhibitors of aspartic, thiol, or metalloproteases. It is maximally active at pH 8 and has a molecular weight of approximately 600,000. This new activity differs from the 720-kDa multicatalytic proteinase, but resembles the soluble ATP-dependent proteolytic system that we previously isolated from murine erythroleukemia cells.
authors.affiliation: Department of Animal Sciences, Rutgers University, New Brunswick, New Jersey 08903.
authors.forename: J M
authors.initials: JM
authors.lastname: Fagan
authors.forename: L
authors.initials: L
authors.lastname: Waxman
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002645:Chickens; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D009113:Muramidase / Q000378:metabolism; D009132:Muscles / Q000201:enzymology*; D010447:Peptide Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D013379:Substrate Specificity; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D011480:Protease Inhibitors; D014452:Ubiquitins; D000255:Adenosine Triphosphate; D009113:Muramidase; D010447:Peptide Hydrolases