G contains an unidentified covalent modification that increases its affinity for adenylyl cyclase

Abstract
Many G protein α subunits are dually acylated with myristate and palmitate or are palmitoylated on more than one cysteine residue near their N termini. The Gα protein that activates adenylyl cyclase, αs, is not myristoylated but can be reversibly palmitoylated. It appears that αs contains another, as-yet-unidentified covalent modification that decreases its apparent dissociation constant for adenylyl cyclase from 50 nM to s does not account for its high affinity for adenylyl cyclase.