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Abstract
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.
Highlights
The availabilityof purified Gall and theG-protein- purified from three different sources and have been shown to regulated phospholipase C from turkey erythrocytes activate phospholipase C in the presence ofA1F; or GTPyS has allowed an examination of the direct effectsof Gprotein &-subunit on the components of the inositol lipid signalingsystem
We previously reported that when reconstituted into turkey erythrocyte ghosts, G-protein Bysubunit inhibited A1F;-promoted activation of phospholipase C and adenylylcyclase,and potentiated Pzy-purinergicreceptor agonist-stimulated phospholipase C activity [18].The mechanism(s1 of effect of Pysubunit was not established, a tacitassumption from such results is that increases in membrane &-subunit con
The concentrationdependence of Gall for activation of turkey erythrocyte phospholipase C and bovine brain phospholipase (2-8, as well as the concentration dependence of the two enzymes for activation by Gall, were very similaIr.n contrast, Tang and Gilman [22] have reported that calmodulin-activated adenylylcyclase is inhibited by G-protein Pysubunit, whereas &-subunit stimulatesthe calmodulin-insensitive type I1 and type IV adenylylcyclases [22, 23]
Summary
The availabilityof purified Gall and theG-protein- purified from three different sources and have been shown to regulated phospholipase C from turkey erythrocytes activate phospholipase C in the presence ofA1F; or GTPyS has allowed an examination of the direct effectsof Gprotein &-subunit on the components of the inositol lipid signalingsystem. Protein Assays-Protein concentrations were estimated as follows: bovine brain &-subunit and phospholipase C-0, and turkey erythrocyte Gall, Bysubunit,and phospholipase C were determined by Amido Black staining [28].
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