1. Reactions of 1,2-naphthaquinone with amino acids, glutathione and proteins of the lens have been studied in connexion with investigations of naphthalene-induced cataract. 2. Cysteine reacts probably through its amino group with 1,2-naphthaquinone to form either purple or brown compounds with characteristic absorption spectra. 3. Glutathione reacts with 1,2-naphthaquinone through its thiol group. 4. Spectroscopic evidence suggests that 1,2-naphthaquinone reacts with the amino group of amino acids. This reaction may take place in the aqueous humour. 5. The proteins of lens react with 1,2-naphthaquinone to form brown compounds. 6. There is loss of protein thiol in this reaction and the products are less easily digestible by pancreatin than normal lens proteins. 7. The compound of alpha-crystallin and 1,2-naphthaquinone is soluble at neutrality, but the compounds of beta-crystallins and of gamma-crystallins are largely insoluble. 8. The brown reaction products of glutathione or cysteine with 1,2-naphthaquinone catalyse the oxidation of ascorbic acid in the same way as 1,2-naphthaquinone itself. 9. These results are discussed in relation to naphthalene-induced cataract.
