Structure of photoreceptive membranes of Drosophila compound eyes as studied by quick-freezing electron microscopy

Photoreceptive membranes of Drosophila compound eyes were studied by quick-freezing electron microscopy. The quick-frozen photoreceptive microvilli appeared cylindrical in shape either when they were freeze-substituted or freeze-fractured. Deep-etch replication revealed the extracellular surfaces of microvilli which were covered by various particles arranged in a helical manner. The protoplasmic surfaces were covered by more regular helical rows of particles about 10 nm in diameter. When rhodopsin content of the photoreceptive membranes was reduced by vitamin A-deficiency, the intramembrane particles drastically decreased resulting in the disappearance of particles in rows. Our results strongly suggest the regular arrangement of rhodopsin molecules in invertebrate photoreceptive membranes.