α-Transducin immunoreactivity in retinae and sensory pineal organs of adult vertebrates

Antiserum against the α subunit of bovine rod-outer-segment transducin was used in an immunocytochemical study that identified the protein in retina (human, baboon, owl monkey, cow, rat, quail, newt, frog, salmon, eel, and lamprey), pineal organ (quail, newt, frog, salmon, eel, and lamprey), and parapineal organ (salmon and lamprey). No reaction was observed in the cow or rat pineal organ or the eel parapineal organ. The immunoreaction was very strong in outer segments but weak in perikarya. Immunoblots of crude tissue extracts of bovine rod-outer-segment membranes and frog and fish retina revealed a 39-kDa immunopositive band. The fish retina also contained two additional bands of mass 43 kDa and 25 kDa. Only the 43-kDa band was present in the fish pineal organ, which is photosensitive. This raises the possibility that the 43-kDa α transducin-immunopositive molecule present in the fish pineal organ and retina may be involved in phototransduction.