title: Why does ribonuclease irreversibly inactivate at high temperatures?
abstract: The mechanism of irreversible thermoinactivation of bovine pancreatic ribonuclease A in the pH range relevant to enzymatic catalysis has been elucidated. At 90 degrees C and pH 4, the enzyme inactivation is caused by hydrolysis of peptide bonds at aspartic acid residues (the main process) and deamidation of asparagine and/or glutamine residues. At 90 degrees C and neutral pH (pH 6 and 8), the enzyme inactivation is caused by a combination of disulfide interchange (the main process), beta-elimination of cystine residues, and deamidation of asparagine and/or glutamine residues. These four processes appear to demarcate the upper limit of thermostability of enzymes.
mesh_terms: D000818:Animals; D002417:Cattle; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011487:Protein Conformation; D011489:Protein Denaturation; D012259:Ribonuclease, Pancreatic / Q000037:antagonists & inhibitors*; D013816:Thermodynamics
chemical_list: D012259:Ribonuclease, Pancreatic