Immunoelectron-microscopic study of G-protein distribution in photoreceptor cells of the cephalopod Sepia officinalis.
Previous studies suggest that more than one single light-stimulated transduction pathway seems to be present in photoreceptor cells of invertebrates. Accordingly, more than one light-dependent G-protein has been detected in squid photoreceptor cells. Two different antibodies were used to locate the distribution of G-proteins in Sepia photoreceptors. One antiserum (anti-G alpha-common) has been raised against the peptide CGAGESGKSTIVKQMK. This sequence is found in most G alpha-protein subunits, it is also present in transducin of vertebrates. This sequence however, is conserved only partially in G alpha q from photosensory membranes of the squid. The second antiserum (anti-G alpha q) has been raised against the peptide QLNLKEYNLV. This sequence is present at the C-terminus of e.g. G alpha q from mouse brain and is identical also in squid. Anti-G alpha q very strongly interacted with the rhabdomeres of the photoreceptor cells from Sepia. In the non-rhabdomeric cytoplasm of the photoreceptor cells gold granules (bound to the second antibody) were almost absent. With anti-G alpha-common, only a small number of gold particles could be found at the rhabdomeres. The non-rhabdomeric cytoplasm was not labelled. Thus, further G-proteins that might be involved in a light dependent phototransduction mechanism besides the phosphoinositide pathway can hardly be expected to belong to the group of 'common' G-proteins.
Schraermeyer
U
U
Institut für Biologie II (Zoologie), RWTH Aachen, Germany.
Stieve
H
H
Rack
M
M
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000276:immunology; D007150:Immunohistochemistry; D007448:Invertebrates; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism* / Q000648:ultrastructure
D000906:Antibodies; D010455:Peptides; D019204:GTP-Binding Proteins