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Activation of the Heat-Stable Polypeptide of the ATP-Dependent Proteolytic System

Aaron Ciechanover, Hannah Heller, Rachel Katz-Etzion and Avram Hershko
Proceedings of the National Academy of Sciences of the United States of America
Vol. 78, No. 2, [Part 2: Biological Sciences] (Feb., 1981), pp. 761-765
Stable URL: http://www.jstor.org/stable/10283
Page Count: 5
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Activation of the Heat-Stable Polypeptide of the ATP-Dependent Proteolytic System
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Abstract

It had been shown previously that the heat-stable polypeptide of the ATP-dependent proteolytic system of reticulocytes, designated APF-1, forms covalent conjugates with protein substrates in an ATP-requiring process. We now describe an enzyme that carries out the activation by ATP of the polypeptide with pyrophosphate displacement. The formation of AMP-polypeptide and transfer of the polypeptide to a secondary acceptor are suggested by an APF-1 requirement for ATP-PPi and ATP-AMP exchange reactions, respectively. With radiolabeled polypeptide, an ATP-dependent labeling of the enzyme was shown to be by a linkage that is acid stable but is labile to treatment with mild alkali, hydroxylamine, borohydride, or mercuric salts. It therefore appears that the AMP-polypeptide undergoes attack by an -SH group of the enzyme to form a thiolester.

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