Aspartic acid racemization: evidence for marked longevity of elastin in human skin.
BACKGROUND
In extracellular proteins, aspartic acid racemization (AAR) has the potential to identify long-lived or permanent proteins.


OBJECTIVE
We present data to show an age-dependent increase in AAR in chronologically aged skin elastin.


METHODS
Elastin was purified in a multistep procedure designed to remove contaminating proteins and to avoid induced racemization. As a control experiment, elastin was also purified from the richest elastin bearing tissue, the yellow ligaments of the spine.


RESULTS
In total skin, specimens displayed a slight age-dependent increase in d-aspartyl residues, but in purified elastin the rate of increase was rapid and highly correlated with age (r = 0.98). Similar rates were observed in the control data from the yellow ligaments. The AAR rates were found to be higher in elastin from skin (and yellow ligaments) than previous studies of lung parenchyma and from aorta had shown. These differences appear to be related to the purity of the extracted elastin product, and to a significant in vivo degradation of elastin in skin.


CONCLUSIONS
The age-dependent accumulation of modified aspartic acid residues appears to be a common feature in ageing elastin, independent of the tissue source. This indicates a lack of turnover and an accumulation of elastin damage in diverse ageing tissues, possibly as part of programmed ageing.
Ritz-Timme
S
S
Institut für Rechtsmedizin der Christian-Albrechts-Universität zu Kiel, Arnold-Heller-Strasse 12, D-24105 Kiel, Germany.
Laumeier
I
I
Collins
M J
MJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D000596:Amino Acids / Q000032:analysis; D001224:Aspartic Acid / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D004549:Elastin / Q000378:metabolism*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D012867:Skin / Q000033:anatomy & histology / Q000378:metabolism*; D015595:Skin Aging / Q000502:physiology; D013237:Stereoisomerism
D000596:Amino Acids; D001224:Aspartic Acid; D004549:Elastin