Selectivity of β-adrenergic receptor kinase 2 for G protein βγ subunits

Phosphorylation of G protein-coupled receptors by β-adrenergic receptor kinases (βARK) requires the presence of G protein βγ subunits. We have investigated the ability of the two βARK isoforms to distinguish between defined recombinant βγ subunits. βARK2 had an about 25% lower specific activity than βARK1 towards rhodopsin and the β2-adrenergic receptor but the two kinases shared the selectivity for βγ subunits: βγ complexes consisting of β1 or β2 in combination with γ2, γ5, and γ7 were more efficacious than those with γ3 or β1γ1. Thus, while βARKs differentiate between defined βγ subunits, βγ complexes do not discriminate between βARK isoforms.