In enzymology, a beta-adrenergic-receptor kinase is an enzyme that catalyzes the chemical reaction: Thus, the two substrates of this enzyme are ATP and beta-adrenergic receptor, whereas its two products are ADP and phospho-beta-adrenergic receptor. This enzyme belongs to the family of transferases, specifically those transferring a phosphate group to the sidechain oxygen atom of serine or threonine residues in proteins (protein-serine/threonine kinases). The systematic name of this enzyme class is ATP:[beta-adrenergic receptor] phosphotransferase. Other names in common use include ATP:beta-adrenergic-receptor phosphotransferase, [beta-adrenergic-receptor] kinase, beta-adrenergic receptor-specific kinase, beta-AR kinase, beta-ARK, beta-ARK 1, beta-ARK 2, beta-receptor kinase, GRK2, GRK3, beta-adrenergic-receptor kinase (phosphorylating), beta2ARK, betaARK1, beta-adrenoceptor kinase, beta-adrenoceptor kinase 1, beta-adrenoceptor kinase 2, ADRBK1, BARK1, adrenergic receptor kinase, and STK15. Several compounds are known to inhibit this enzyme, including Zinc, and Digitonin.