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Mammalian eye lens represents a suitable model system for studying the age-related post-translational modifications of proteins. Eye lens is a transparent biconvex body located between the aqueous humor and vitreous body. As reported in Fig. 1, the bulk of the lens consists of a single cell type (the lens fiber) concentrically arranged by age, which derives from the epithelium located at the anterior surface of the lens, underneath the capsule. At the equator the epithelial cells cease to divide and differentiate into the ribbon-like fiber cells. Lens fiber maturation is accompanied by the loss of both nucleus and organelles; as a consequence, protein synthesis is not longer operative after differentiation. New fibers are always laid down at the periphery (cortex); thus progressively older fibers are found as one moves axially toward the center of the tissue (nucleus). Since no cell is ever sloughed from the lens, the nuclear fibers are those formed during the embryogenesis and their proteins can reach exceptionally high ages (1).