Squid photoreceptor phospholipase C is stimulated by membrane Gq alpha but not by soluble Gq alpha.
Phospholipase C (PLC) was purified from squid retina. Soluble Gq alpha, membrane Gq alpha and G beta gamma were isolated from GTP gamma S-treated and light-illuminated photoreceptor membranes. The membrane Gq alpha stimulated phosphatidyl inositol-phospholipase C (PI-PLC) activity in a dose-dependent manner. Soluble Gq alpha and membrane G beta gamma showed no stimulating effects on PLC. GTP gamma S-binding was found exclusively in membrane fraction, with very little present in the KCl-soluble fraction which contained soluble Gq alpha. These results indicate that light-activated rhodopsin activates PLC through membrane-bound Gq alpha and suggest that the rhodopsin/Gq/PLC cascade might be the pathway of phototransduction in squid photoreceptors.
Department of Pharmacology, Hyogo College of Medicine, Japan.
T
T
Suzuki
A
A
Terakita
K
K
Narita
K
K
Nagai
Y
Y
Tsukahara
Y
Y
Kito
D000818:Animals; D049832:Decapodiformes; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate / Q000201:enzymology*; D011487:Protein Conformation; D015398:Signal Transduction; D012995:Solubility; D013347:Subcellular Fractions / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism*
D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010738:Type C Phospholipases; D019204:GTP-Binding Proteins