Beta gamma-subunit activation of G-protein-regulated phospholipase C.
The availability of purified G alpha 11 and the G-protein-regulated phospholipase C from turkey erythrocytes has allowed an examination of the direct effects of G-protein beta gamma-subunit on the components of the inositol lipid signaling system. Reconstitution of purified turkey erythrocyte or bovine brain beta gamma-subunit into phospholipid vesicles containing G alpha 11 inhibited AlF4- induced activation of phospholipase C. However, beta gamma-subunit at higher concentrations increased phospholipase C activity. This stimulatory effect of beta gamma-subunit on phospholipase C did not require the presence of the alpha-subunit. G alpha o had no effect on the catalytic activity of phospholipase C. However, coreconstitution of G alpha o and beta gamma-subunit shifted to the right the concentration-effect curve for beta gamma-subunit-promoted activation of phospholipase C. As was observed with G alpha 11, the increase in activity observed in the presence of beta gamma-subunit occurred as an increase in the maximal activity and with no change in the apparent affinity for Ca2+ for phospholipase C activation. The concentration dependence of G alpha 11 for activation of turkey erythrocyte phospholipase C and bovine brain phospholipase C-beta, as well as the concentration dependence of the two enzymes for activation by G alpha 11, were very similar. In contrast, beta gamma-subunit was a much less effective activator of bovine brain phospholipase C-beta than the turkey erythrocyte enzyme. The observation of direct effects of free beta gamma-subunit on phospholipase C extend the possibilities for receptor-mediated regulation of this signaling pathway.
Boyer
J L
JL
Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill 27599.
Waldo
G L
GL
Harden
T K
TK
D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004912:Erythrocytes / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D015398:Signal Transduction; D013997:Time Factors; D014422:Turkeys; D010738:Type C Phospholipases / Q000097:blood* / Q000302:isolation & purification
D046911:Macromolecular Substances; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium