Concanavalin A receptor(s) possibly interacts with at least two kinds of GTP-binding proteins in murine thymocytes.
A part of the GTP gamma S-binding activity in murine thymocyte membranes was found to have affinity to a concanavalin A (Con A)-Sepharose column. The material was identified as Gi (inhibitory GTP-binding protein) on the basis of the molecular weight and by islet activating protein-dependent ADP-ribosylation and anti-alpha i (alpha subunit of Gi) immunoblotting. However, when the membranes prepared from Con A-stimulated thymocytes were used, no GTP gamma S-binding activity was detected in the Con A-bound fraction, suggesting that Gi physically and specifically associated with Con A acceptors dissociates upon Con A stimulation. Furthermore, another GTP gamma S-binding protein (25 kDa), which is quite similar to a novel phosphoinositide-specific phospholipase C (PI-PLC)-associated G protein in calf thymocytes (Wang, P., Toyoshima, S., & Osawa, T. (1988) J. Biochem. 103, 137-142), was detected among the Con A-Sepharose-bound proteins with the chemical cross-linking technique. When the 40 kDa and 25 kDa G proteins associated with Con A receptor(s) were isolated and their direct effects on the activity of partially purified PI-PLC as to phosphatidylinositol 4,5-bisphosphate hydrolysis were examined, the 25 kDa G protein was found to enhance the PI-PLC activity more effectively. On the other hand, pretreatment of cells with islet-activating protein completely abolished the inhibitory effect of Con A on the prostaglandin E1 and isoproterenol-induced increases of cellular cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)
Wang
P
P
Division of Chemical Toxicology and Immunochemistry, Faculty of Pharmaceutical Sciences, University of Tokyo.
Matsumoto
N
N
Toyoshima
S
S
Osawa
T
T
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002846:Chromatography, Affinity; D003208:Concanavalin A / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D051379:Mice; D011952:Receptors, Concanavalin A / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology* / Q000378:metabolism
D011952:Receptors, Concanavalin A; D003208:Concanavalin A; D000242:Cyclic AMP; D019204:GTP-Binding Proteins