A Light-catalysed Reaction in the Aqueous Humour of the Eye

Abstract

Kon and Watson¹ found that ascorbic acid in milk was destroyed by light and Hopkins² showed that this destruction was caused by the photocatalytic oxidation of ascorbic acid by riboflavin. Oxygen was necessary and peroxide was formed. In connexion with an examination of glutathione peroxidase of lens I became interested in the ascorbic acid of the aqueous humour as a possible source of hydrogen peroxide. In many mammals, including man, the level of ascorbic acid in the aqueous humour is about 1.0 mM, which is far higher than the level in serum³. Light freely penetrates through the aqueous humour whenever the eye is open, and Philpot and Pirie⁴ found traces of riboflavin and/or flavinadenine dinucleotide in the aqueous humour of cattle eyes. It seemed possible, therefore, that a photocatalysed oxidation of ascorbic acid might take place in the eye in vivo, as it does in milk in vitro.