Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ubiquitin-lysozyme conjugates have been used as substrates to identify an ATP-dependent protease from rabbit reticulocyte lysates. The enzyme, which has been partially purified by DEAE chromatography and glycerol gradient centrifugation, has an apparent molecular weight greater than 600,000 based on sedimentation and gel filtration. Whereas it degrades conjugated lysozyme molecules in the presence of ATP, the protease does not degrade free lysozyme molecules even upon addition of ubiquitin, lysozyme-ubiquitin conjugates, and ATP. Degradation of lysozyme conjugates is independent of added ubiquitin and occurs in fractions incapable of ubiquitin conjugation. Proteolysis is maximal at pH 7.8, inhibited by hemin, N-ethylmaleimide, or aurintricarboxylic acid, and proceeds with an apparent Arrhenius activation energy in the range of 27 +/- 5 kcal/mol. These properties are similar to those observed for the degradation of lysozyme conjugates in lysates indicating that the partially purified protease catalyzes the "second" ATP-utilizing reaction identified previously (Hough, R., and Rechsteiner, M. (1984) Proc. Natl. Acad. Sci. U. S. A. 81, 90-94; Hershko, A., Leshinsky, E., Ganoth, D., and Heller, H. (1984) Proc. Natl. Acad. Sci. U. S. A. 81, 1619-1623; Tanaka, K., Waxman, L., and Goldberg, A. L. (1983) J. Cell Biol. 96, 1580-1585).
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PMID:Ubiquitin-lysozyme conjugates. Identification and characterization of an ATP-dependent protease from rabbit reticulocyte lysates. 300 14

Xenopus egg extract is capable of supporting mitosis in vitro, which makes it ideal for biochemical analysis of the cell cycle. Since several studies have implicated the ubiquitin system in cell cycle progression, we have measured ubiquitin conjugation rates, proteolysis of ubiquitin-lysozyme conjugates, and rates of isopeptidase activity in cycling Xenopus egg extracts. Although ubiquitin conjugation in cytostatic factor arrested extract was half that in activated extract, there were no changes in rates of ubiquitin conjugation during the cell cycle. Ubiquitin conjugates are degraded by a 26 S ATP-stimulated protease. The ability of the 26 S protease to degrade ubiquitin-lysozyme conjugates and a fluorigenic peptide also remained constant across the cell cycle. In contrast to previously characterized systems, isopeptidase activity in Xenopus egg extract is energy-dependent. Glycerol gradient fractionation of Xenopus egg extract separated two ATP-dependent isopeptidases. On co-sedimented with the 26 S protease; the other sedimented slower and was not associated with any additional proteolytic activity. As found for rates of Ub conjugation and conjugate proteolysis, there was little or no variation in isopeptidase activity during the cell cycle.
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PMID:Ubiquitin metabolism in cycling Xenopus egg extracts. 840 56