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With an amino acid analyzer, we measured amino acids and related compounds in serum and aqueous humor from normal Chinese and some patients with extreme myopia or senile cataracts. Forty peaks were well resolved, and their areas were used to quantify each compound. In the myopic patients, glutamate, alpha-aminoadipate, and methionine concentrations in serum were 10-fold those in the normal subjects. Values for most of the other amino acids and related compounds were also higher in myopic patients' sera. In the cataract patients, concentrations of most of these compounds were lower in serum but higher in aqueous humor than for the normal subjects. Tryptophan was present in significant amounts in sera from the normal subjects, but was not detectable in the senile-cataract patients. The ratio of amino acid concentration in aqueous humor to that in the serum (Ch/Cs) was higher in the cataract patients than in normal subjects for almost all of the compounds we measured.

All biomacromolecules are faced with oxidative stress. Oxidation of a protein molecule always induces inactivation of the molecule and introduces a tag to that molecule. These modified protein molecules are prone to degradation in vivo by the proteasome system. Coupling of protein modification and degradation of chemically modified proteins is one of the normal protein turnover pathways in vivo. We call this a ‘chemical apoptosis’ process, which is one of the early manifestations of programmed cell death. Impairment of the proteasome system leads to accumulation of modified nonfunctional proteins or ‘aged proteins’ that might cause various clinical syndromes including cataractogenesis, premature aging, neurological degeneration and rheumatoid disease. The metal-catalyzed oxidation of biomacromolecules provides an excellent artificial aging system in vitro. The system is very useful in the characterization of structure and function relationships of proteins (enzymes), especially in those containing metal binding domain(s), because the oxidation is always followed by an affinity cleavage at the metal binding site(s) that allows easy identification and further characterization.

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