In enzymology, a myosin-heavy-chain kinase is an enzyme that catalyzes the chemical reaction Thus, the two substrates of this enzyme are ATP and myosin heavy-chain, whereas its two products are ADP and myosin heavy-chain phosphate. 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:[myosin heavy-chain] O-phosphotransferase. Other names in common use include