title: Skeletal muscle and liver contain a soluble ATP + ubiquitin-dependent proteolytic system.
abstract: Although protein breakdown in most cells seems to require metabolic energy, it has only been possible to establish a soluble ATP-dependent proteolytic system in extracts of reticulocytes and erythroleukemia cells. We have now succeeded in demonstrating in soluble extracts and more purified preparations from rabbit skeletal muscle a 12-fold stimulation by ATP of breakdown of endogenous proteins and a 6-fold stimulation of 125I-lysozyme degradation. However, it has still not been possible to demonstrate such large effects of ATP in similar preparations from liver. Nevertheless, after fractionation by DEAE-chromatography and gel filtration, we found that extracts from liver as well as muscle contain both the enzymes which conjugate ubiquitin to 125I-lysozyme and an enzyme which specifically degrades the ubiquitin-protein conjugates. When this proteolytic activity was recombined with the conjugating enzymes, ATP + ubiquitin-dependent degradation of many proteins was observed. This proteinase is unusually large, approx. 1500 kDa, requires ATP hydrolysis for activity and resembles the ubiquitin-protein-conjugate degrading activity isolated from reticulocytes. Thus the ATP + ubiquitin-dependent pathway is likely to be present in all mammalian cells, although certain tissues may contain inhibitory factors.
authors.forename: J M
authors.initials: JM
authors.lastname: Fagan
authors.forename: L
authors.initials: L
authors.lastname: Waxman
authors.forename: A L
authors.initials: AL
authors.lastname: Goldberg
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D010447:Peptide Hydrolases / Q000302:isolation & purification* / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism; D011817:Rabbits; D014452:Ubiquitins / Q000494:pharmacology*
chemical_list: D009124:Muscle Proteins; D011480:Protease Inhibitors; D011506:Proteins; D014452:Ubiquitins; D000255:Adenosine Triphosphate; D010447:Peptide Hydrolases