Degree Name

Doctor of Philosophy


Department of Chemistry


The most common cause for human bhndness is cataract. Surgery is the only available treatment and the cause of cataract is unknown. The aim of this project was to determine if a difference could be discerned in the metabohsm of the essential amino acid, tryptophan in cataract patients compared with normal controls. To investigate this aspect an oral tryptophan loading protocol was used. In order to assess the response of tryptophan metabolites to the load an HPLC technique with dual electrochemical and fluorescence detection was developed which could simultaneously measure tryptophan and seven of its metabolites. Serum samples were analysed at 0, 1, 2, 4 and 6 hours for total and free tryptophan, 5-hydroxyanthranilic acid, 3-hydroxyanthranilic acid, kynurenine, kynurenic acid, xanthurenic acid, anthranilic acid and 5-hydroxytryptophan. Statistically significant differences were found. An increased response to Üie tryptophan load was found in cataract patients for two metabolites, kynurenine and 5-hydroxyanthranilic acid. A diminished response was found for kynurenic acid and total tryptophan. From the data it appeared that there may be two or more sub-groups of cataract patients who metabolise tryptophan differently from controls. Since it has been shown recently that certain aminophenolic metabolites of tryptophan can modify lens proteins and thereby mimic cataract formation, the finding of a difference in tryptophan metabolism in cataract patients may represent a significant step in the quest for a biochemical basis for this disease.