Old Proteins in Man: A Field in its Infancy.

It has only recently been appreciated that the human body contains many long-lived proteins (LLPs). Their gradual degradation over time contributes to human aging and probably also to a range of age-related disorders. Indeed, the role of progressive damage of proteins in aging may be indicated by the fact that many neurological diseases do not appear until after middle age. A major factor responsible for the deterioration of old proteins is the spontaneous breakdown of susceptible amino acid residues resulting in racemization, truncation, deamidation, and crosslinking. When proteins decompose in this way, their structures and functions may be altered and novel epitopes can be formed that can induce an autoimmune response.