title: Activation of the heat-stable polypeptide of the ATP-dependent proteolytic system.
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.
mesh_terms: D000255:Adenosine Triphosphate; D000818:Animals; D002868:Chromosomal Proteins, Non-Histone / Q000097:blood* / Q000302:isolation & purification; D011756:Diphosphates; D004355:Drug Stability; D007700:Kinetics; D010455:Peptides / Q000097:blood; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism*; D013379:Substrate Specificity; D014452:Ubiquitins
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D011756:Diphosphates; D010455:Peptides; D014452:Ubiquitins; D000255:Adenosine Triphosphate