On the existence of γ-crystallin in the bird lens

Sauropsidans until recently were acknowledged to possess the lens-specific proteins, α and β-crystallins, while lacking γ-crystallins. The γ-crystallins have been employed as specific indicators of normal and regenerating lens fiber cell differentiation in several other organisms. It has been reported, however, that indeed, birds do possess γ-crystallins, and that furthermore this protein is not lens-fiber specific, since it could be found in annular pad and epithelium as well as fibers. Several physical characteristics of this protein cited by those suggesting its existence and at odds with those known for γ-crystallins, led the authors to further investigate the putative γ-crystallin. Pigeon “γ”-crystallin was prepared exactly according to previously published methods, and subjected to amino acid and N-terminal analyses, and peptide mapping. The fraction isolated satisfied none of the commonly-accepted criteria for γ-crystallins. Thus the pigeon “γ”-crystallin did not exhibit low values for alanine and lysine; a free N-terminal amino acid could not be detected; and peptide mapping did not reveal the distinctive peptide of γ-crystallins, the fastest moving orange spot in the electrophoresis direction. The bird lens, then, does not contain γ-crystallin; the γ-crystallins, when present, remain as reliable indicators of lens fiber differentiation.