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Increase in ubiquitin-protein conjugates concomitant with the increase in proteolysis in rat skeletal muscle during starvation and atrophy denervationThe rapid loss of skeletal-muscle protein during starvation and after denervation occurs primarily through increased rates of protein breakdown and activation of a non-lysosomal ATP-dependent proteolytic process. To investigate whether protein flux through the ubiquitin (Ub)-proteasome pathway is enhanced, as was suggested by related studies, we measured, using specific polyclonal antibodies, the levels of Ub-conjugated proteins in normal and atrophying muscles. The content of these critical intermediates had increased 50-250% after food deprivation in the extensor digitorum longus and soleus muscles 2 days after denervation. Like rates of proteolysis, the amount of Ub-protein conjugates and the fraction of Ub conjugated to proteins increased progressively during food deprivation and returned to normal within 1 day of refeeding. During starvation, muscles of adrenalectomized rats failed to increase protein breakdown, and they showed 50% lower levels of Ub-protein conjugates than those of starved control animals. The changes in the pools of Ub-conjugated proteins (the substrates for the 26S proteasome) thus coincided with and can account for the alterations in overall proteolysis. In this pathway, large multiubiquitinated proteins are preferentially degraded, and the Ub-protein conjugates that accumulated in atrophying muscles were of high molecular mass (> 100 kDa). When innervated and denervated gastrocnemius muscles were fractionated, a significant increase in ubiquitinated proteins was found in the myofibrillar fraction, the proteins of which are preferentially degraded on denervation, but not in the soluble fraction. Thus activation of this proteolytic pathway in atrophying muscles probably occurs initially by increasing Ub conjugation to cell proteins. The resulting accumulation of Ub-protein conjugates suggests that their degradation by the 26S proteasome complex subsequently becomes rate-limiting in these catabolic states.
Document ID
20050000194
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Wing, S. S.
(Harvard Medical School Boston, MA 02115, United States)
Haas, A. L.
Goldberg, A. L.
Date Acquired
August 22, 2013
Publication Date
May 1, 1995
Publication Information
Publication: The Biochemical journal
Volume: 307 ( Pt 3)
ISSN: 0264-6021
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Number 40-40
NASA Program Space Biology
NASA Discipline Musculoskeletal
Non-NASA Center

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