Alterations in the structure of proteins that cause their irreversible inactivation.

A variety of changes in environmental conditions (temperature, pH, salts, solvents, etc.) can cause protein inactivation. However, the mechanisms of irreversible protein inactivation often follow common pathways. Using heat stress as an example, the conformational and covalent processes leading to the irreversible thermo-inactivation of enzymes will be described. In particular, work in our laboratory has identified several chemical reactions which contribute to enzyme thermo-inactivation: cystine destruction, thiol-catalysed disulfide interchange, oxidation of cysteine residues, deamidation of asparagine and glutamine residues, and hydrolysis of peptide bonds at aspartic acid residues. Implications of this work for the stability of proteins during, and following, the lyophilization process will be addressed.