Evidence for involvement of guanine nucleotide-binding regulatory proteins in the activation of phospholipases by hormones.

Guanine nucleotide-binding regulatory proteins similar to Gs and Gi may be involved in the activation of phospholipases C and A2 by hormones and other ligands. The binding of hormones to receptors that activate phospholipase C is decreased by guanine nucleotides and these hormones also stimulate a high-affinity GTPase activity in cell membranes. Effects of hormones on phospholipase C activity in cell-free preparations are dependent on the presence of guanine nucleotides. In addition, fluoride and nonhydrolyzable GTP analogs activate phospholipases in a manner that can be blocked by GDP beta S. The putative guanine nucleotide-binding regulatory protein that appears to be involved in activation of phospholipase C is sensitive to pertussis toxin in some cells but not in others.