Light-induced phosphorylation of retina-specific polypeptides of Drosophila in vivo.

A moderate light stimulus induced isoelectric point (pI) changes in three classes of retina-specific polypeptides (80, 49, and 39 kilodaltons) of Drosophila in vivo. When inorganic phosphate labeled with phosphorus-32 was fed to flies, the radioactive label was incorporated into these polypeptides during the pI changes, indicating light-induced phosphorylation of the polypeptides. A 1-millisecond flash induced a detectable amount of phosphorylation in the 80- and 49-kilodalton polypeptides within 3 seconds. These results, and our previous results with norpA mutants, suggest that phosphorylation of these two polypeptides may be involved in some early stages of photoreceptor excitation or its modulation.