Selective oxidation of cysteine and methionine in normal and senile cataractous lenses.

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Abstract
The oxidation state of methionine and cysteine in normal and cataractous human lenses is reported. In young lenses no oxidation was detected in any protein fraction examined. Only the intrinsic membrane fraction and membrane-related components showed evidence of oxidation in old (60-65 yr of age) normal lenses. In a similar age group, with the development of cataract, progressive, dramatic changes were observed. With severe cataracts, 60% or more of the methionine in membrane-associated components was found in the methionine sulfoxide form; methionine sulfone was observed in 1 case. Most of the cysteine was found oxidized to the disulfide form or putative cysteic acid. Mixed disulfides with glutathione were observed. Oxidative changes in soluble components as illustrated by .alpha.-crystallin occurred more gradually. Extensive oxidation of lens proteins apparently occurs with cataract and begins at the lens fiber membrane.