Pteridines and purines as major pigments of the avian iris

Stromal pigments from the irises of 28 species of birds having brightly colored eyes were extracted and analyzed. Carotenoids were present in six species and they were the sole bright pigment in only two of these. The iris pigments of the majority of the birds examined were soluble in 0.1 M NaOH and chromatographic analysis indicated they were primarily pteridines and purines. The pteridines often occurred in a crystalline state, either alone or, more commonly, in conjunction with purines.