The necessity of protein purification in non-dental tissues for accurate results can be attributed to the more complex biochemical compositions of non-dental tissues and/or to their lower contents of metabolically stable proteins, as compared with dentine.
In contrast to the non-dental tissues investigated so far, the yellow ligaments of the spine exhibit a less complex structure and a high content of long-living protein. The unique composition of these ligaments is characterized by an extremely high content of elastic fibres, they consist of ca. 80% elastic fibres and ca. 20% collagen fibres (Viejo- Fuertes et al. 1998). The major component of the elastic fibres is elastin (comprising up to 90% of the mature fibre), which appears to be an extremely long-living, if not permanent protein of the human organism. Shapiro et al. (1991) and Powell et al. (1992) both observed an age-dependent accumulation of D-aspartic acid in elastin, purified from lung parenchyma and arteries, respectively. The close relationship between AAR and age indicates a life- time residence for mature elastin in human lung parenchyma and arteries (for details see Ritz-Timme and Collins 2002). It could be assumed that elastin is permanent and exhibits an in vivo racemization also in the bradytrophic yellow ligaments. If this is true, the yellow ligaments with their extremely high content of elastin may represent a tis- sue well suited for age estimation based on AAR.
To test this assumption, AAR was determined in total tissue samples and purified elastin from yellow ligaments of individuals of known age.