GRK3: ProductsG protein-coupled receptor kinases (GRKs) are important modulators of G protein-coupled receptor (GPCR) signaling. Receptor phosphorylation by specific GRKs plays a key role in triggering rapid desensitization. The GRK family consists of 7 isoforms that share a central catalytic domain with homology to other serine/threonine kinases. The catalytic domain is flanked by an amino-terminal RGS domain of 183 - 188 amino acids and a carboxyl-terminus of variable length. GRK1 and GRK7 are members of the rhodopsin kinase or visual GRK subfamily.