In enzymology, a homoserine kinase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are ATP and L-homoserine, whereas its two products are ADP and O-phospho-L-homoserine.
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with an alcohol group as acceptor. The systematic name of this enzyme class is ATP:L-homoserine O-phosphotransferase. Other names in common use include homoserine kinase (phosphorylating), and HSK. This enzyme participates in glycine, serine and threonine metabolism.
As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes , , , , , and .