title: Effects of temperature on the degradation of proteins in rabbit reticulocyte lysates and after injection into HeLa cells.
abstract: Bovine serum albumin, pyruvate kinase, hemoglobin, and the Fc fragment of IgG were labeled and introduced into HeLa cells by erythrocyte-mediated microinjection. Degradation of the injected proteins was then measured in cells cultured at temperatures between 6 degrees C and 37 degrees C. Arrhenius plots revealed a constant Ea of 27 +/- 5 kcal/mol over this temperature interval. Similarly, the apparent Ea for the degradation of long-term endogenously labeled HeLa proteins was 22-26 kcal/mol. Both local protein unfolding and proteolysis by defined enzymes, such as trypsin or papain, proceed with EaS between 5 and 15 kcal/mol. The 2-fold higher values obtained in this study indicate that protein unfolding or simple proteolysis is not rate limiting in the degradation of injected or long-lived endogenous HeLa proteins. Moreover, the relatively uniform EaS suggest that a similar biochemical event is rate limiting in the degradation of a specific protein independent of its half-life. This event may involve a reaction in the ATP-dependent proteolytic pathway from rabbit reticulocyte lysates because we observed that EaS for ATP-dependent proteolysis in this system were also 27 +/- 5 kcal/mol.
mesh_terms: D000818:Animals; D006367:HeLa Cells / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007141:Immunoglobulin Fc Fragments; D007700:Kinetics; D051379:Mice; D008845:Microinjections; D009113:Muramidase / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D011506:Proteins / Q000008:administration & dosage / Q000378:metabolism*; D011770:Pyruvate Kinase / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D006454:Hemoglobins; D007141:Immunoglobulin Fc Fragments; D011506:Proteins; D012710:Serum Albumin, Bovine; D011770:Pyruvate Kinase; D009113:Muramidase; D010447:Peptide Hydrolases