Localization of D-β-Aspartic Acid–Containing Proteins in Human Eyes

Collapse of Homochirality of Amino Acids in Proteins from Various Tissues during Aging

“…Eye. d-b-Asp-Containing proteins were observed in non-pigmented ciliary epithelial cells, drusen, Bruch membrane, and sclera of the human eye [17].…”

“…However, d-Asp residues have been detected in various human tissues such as lens of the eye [2 -5], brain [6 -10], skin [11], teeth [12], bone [13] [14], aorta [15], and ligament [16]. In addition, we recently observed d-Asp in the retina [17], conjunctivae [18], and cornea [19] of the eye, as well as in cardiac muscle, blood vessels of the lung, chief cells of the stomach, longitudinal, and circular muscles of the stomach, and small and large intestines [20] (see Table 1). Aspartic acid is the most easily racemizable amino acid, and d-Asp may be formed by racemization in metabolically inert tissues during the natural aging process.…”

d-Aspartate—An important bioactive substance in mammals: A review from an analytical and biological point of view

“…On the other hand, free d-Asp can be derived from d-aspartyl residue-containing proteins. It is known that l-asparaginyl and l-aspartyl residues in proteins undergo spontaneous isomerization under physiological conditions to generate d-aspartyl and/or isoaspartyl residues [76][77][78][79][80][81][82][83][84][85][86]. In addition, d-aspartyl endopeptidase, a protease that can generate free d-Asp through the degradation of d-aspartyl residuecontaining proteins, has been identified in rabbit and mouse [87].…”

UV B-irradiation enhances the racemization and isomerizaiton of aspartyl residues and production of Nɛ-carboxymethyl lysine (CML) in keratin of skin

“…Biologically uncommon D-aspartyl (Asp) residues have been reported in proteins of various tissues such as tooth [1], eye lens [2,3], retina [4], conjunctivae [4], cornea [4], skin [5], aorta [6], and brain [7] in elderly humans. Aspartic acid is the most easily racemizable amino acid and D-Asp may be formed by racemization in metabolically inactive tissues during the chronological aging process.…”