Ascorbic acid mediated alteration of alpha-crystallin secondary structure

Glycation, the non-enzymatic addition of sugar or other carbonyl compounds to the amino groups of a protein, has been shown to occur with a variety of sugars and a diverse group of proteins. This type of alteration is believed to be an important component of aging for lens proteins and perhaps in cataractogenesis. Glycation has been shown to alter function and spectroscopic techniques have shown that in many cases conformational changes have occurred. Circular dichroism spectroscopy has documented modifications to alpha-crystallin tertiary structure induced by glucose and glucose 6-phosphate but generally no change to secondary structure. Ascorbate and is oxidized derivative dehydroascorbate have been shown to be powerful glycating agents as well as forming cross-links between peptide chains. In this study, alpha-crystallin incubated with ascorbic acid for one or two wk shows significant incorporation of ascorbate, non-reducible cross-links between the protein chains and altered CD spectra in the far UV region indicative of secondary structure modification.