Nonenzymic Posttranslational Modification of Lens Proteins in Aging
Many proteins are modified after translation by reactions catalyzed and controlled by enzymes. Phosphorylation, glycosylation, acetylation, hydroxyla-tions, and other changes are well known to biochemists in different fields. Apart from these changes proteins are thought of as relatively inert, surviving unchanged until removal by proteolysis and replacement, but proteins consist of amino acids, many of which have reactive groups in their side chains: thiols, amides, indoles, imidazoles, phenols, thioethers, and amino and guanidino groups. Furthermore, they exist in an environment containing many reactive small molecules including sugars, reactive metabolites, cyanate derived from urea, corticosteroids, acetaldehyde, and other aldehydes. All of these can attack proteins in vivo in reactions that do not require enzymes. These nonenzymic reactions of active groups on proteins with surrounding molecules are the subject of this chapter.
KeywordsPeripheral Neuropathy Lens Protein Senile Cataract Bovine Lens Isocyanic Acid
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