AMINO-ACID COMPOSITION OF NORMAL AND CATARACTOUS HUMAN LENS PROTEINS

The most significant change observed in the amino acid composition of cataractous lens proteins was in the content of cysteine (-SH) and half-cystine (-S-S-) residues. Normal lenses showed approximately 16 residues of cysteine and 1 half-cystine, whereas fully cataractous lenses showed approximately 2 residues of cysteine and 13 residues of half-cystine per 1000 amino acid residues. The content of tyrosine, histidine and tryptophan in normal and cataractous lenses was not significantly different. The autoxidation of -SH groups appears to be a major chemical change in the cataractogenic process.