Formation of N'-formylkynurenine in proteins from lens and other sources by exposure to sunlight.

The photo-oxidative effect of sunlight on the tryptophan residues of proteins and on free tryptophan is described. Evidence is presented that the indole ring is split to yield N'-formylkynurenine. The possible relation of this photo-oxidative change to changes in the lens proteins of brown cataracts is discussed.