Pteridines as reflecting pigments and components of reflecting organelles in vertebrates.

This paper reviews evidence for the presence of pteridines in iridophores, leucophores, and xanthophores in a wide variety of vertebrate chromatophores, and argues that the chemical and functional distinction between pterinosomes and reflecting platelets is not as clear-cut as previously believed. Observations indicate that: (1) Pteridines may, either alone or in conjunction with purines, form pigment granules that reflect light, (2) these pigment granules are highly variable ranging from fibrous pterinosomes to typical reflecting platelets and may be colored, reflect white light, or be iridescent, and (3) many "leucophores" probably contain typical pterinosomes and presumed associated colorless pteridines and are therefore more closely related to erythrophores and xanthophores than to iridophores with which they are usually classified. We propose that the classification of pigment cells should be modified to reflect these facts.