Oxidation of protein substituents

All the constituent amino acid sidechains in proteins are susceptible to attack by oxidants and free radicals, but some are more vulnerable than others. Thus, exposure of proteins to free radical-generating systems may induce tertiary structural changes as a consequence of modifications to individual amino acid sidechains. As secondary structure is stabilised by hydrogen bonding between peptide groups, interactions of radical species with the polypeptide backbone and interference with the functional groups of the peptide bonds may cause secondary structural modifications. Disruption of the secondary structure may also occur under certain conditions of free radical attack at the a-carbon atom of the peptide bond [20], 

Radical generation at inappropriate sites may thus lead to protein destruction since they are also critical targets for free radical attack, both intracellularly and extracellularly. Proteins may be directly damaged, by specific interactions of oxidants or free radicals with particularly susceptible amino acids. Several amino acyl constituents crucial for a protein s function are particularly vulnerable to radical damage (Fig. 4) [21,22]. 

Hypochlorite, released from inflammatory cells, can induce the inactivation of a i-antiproteinase by oxidising a crucial methionine residue at the active centre of the enzyme. Inactivation of the a j-proteinase inhibitor may allow proteases 

Protein modification via carbonyl interaction has been described in diabetes. There are two modes of modification by glucose  

Glucose is considered to be toxic by virtue of its ability to behave chemically as an aldehyde and is known to form chemically reversible early glycosylation products with protein at a rate proportional to the glucose concentration. 

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