Protein damage in the ageing process: Advances in quantitation and the importance of enzymatic defences Mingzhan Xue, Antonysunil Adaikalakoteswari, Naila Rabbani and

Glycation is a major cause of spontaneous damage to cellular and extracellular proteins in physiological systems, accounting for 0.1-0.2% of lysine and arginine residues (Thornalley, 1999; Thornalley et al., 2003). For some proteins with limited protein turnover, such as those in lens fibre cells, the extent of protein glycation may be up to 10-fold higher (Ahmed et al., 2003). Glycation adducts occur in proteins of tissues and body fluids as glycated amino-acid residues, formed by glycation of proteins in situ.