Table 1.
Chemical instability in proteins.
| Chemical instability | Mechanism | Proteins | Reference |
|---|---|---|---|
| Deamidation | The hydrolysis of Asparagine (Asn) and Glutamine (Gln) | Human growth hormone (hGH), Insulin, γ-Globulin, Hemoglobin | |
| Isomerization of Asp | The option cyclic imide intermediates to form either Aspartate (Asp) or iso-Asp products | Monoclonal Antibodies (MAbs) | 17–18 |
| Hydrolysis of Asp | Asp-associated hydrolysis of the peptide backbone | Nerve growth factor (NGF) | 17, 23 |
| Hinge region hydrolysis | Hydrolysis of the peptide backbone within the hinge region of antibody | MAbs | 17–19 |
| Hydrolysis of Trp | Hydrolysis of Tryptophan (Trp) to kynurenine and related substances | Myofibrillar proteins | 17, 21 |
| Racemization and β-elimination | Deprotonation of the hydrogen on the α-carbon | Murine lysozyme, IL-1ra, Myelin in muscle | |
| Diketopiperazine (DKP) formation | Amine attack the second carbonyl group in the peptide backbone and formation of DKP ring | Human growth hormone (hGH) | 17, 23 |
| Glycation of Proteins | The reaction with a base, typically the side chain of lysine and a carbonyl group of a reducing sugar | Hemoglobin, Immunoglobulin G2 (IgG2s) | |
| Formation of pGlu | Nucleophilic attack of the N-terminal amine on the side chain of a Glutamic acid (Glu) residue (and occasionally a Gln residue) to form a five membered ring structure | Bone morphogenetic protein 15 (BMP15) | 17–21 |
| Disulfide scrambling | Removal of free Cystine (Cys) residues (the reduced form), which can act as the starting point for disulfide scrambling or exchange | IgG2s | 17–18 |
| Oxidations: | |||
| Oxidation of Met | Oxidation of Met accomplished with a wide range of ROS and pH | MAbs | 17, 25 |
| Metal-catalyzed oxidation (MCO) | Binding of redox active metal to a protein amino acids (often Gly, Asp, His, and Cys) | Human relaxin, Prolastin, Human growth hormone | 17–23 |
| Oxidation of Trp | Oxidation of Trp residue | MAbs | 17–21 |
| Photooxidation | Chemical oxidation of light sensitive amino acids e.g. Trp, tyrosine (Tyr), and Phenylalanine (Phe) | MAbs, Milk proteins | 17–26 |
| Cysteine Oxidation | Oxidative process involving Cys residues | Alcohol dehydrogenase | 17, 26 |