GALK2 (galactokinase 2) is a GHMP family kinase that phosphorylates N-acetylgalactosamine (GalNAc) using ATP as the phosphate donor, with kinetic parameters of Km(ATP) = 14 ± 3 μM, Km(GalNAc) = 40 ± 14 μM, and kcat = 1.0 ± 0.1 s⁻¹ 1. The enzyme operates via an ordered ternary complex mechanism with ATP binding first 1. GALK2 functions as a key component of the galactose/GalNAc salvage pathway, enabling cells to reutilize free GalNAc derived from complex carbohydrate degradation and generate UDP-galactose for O-linked glycosylation 2. When GALK2 is disrupted alongside UDP-galactose-4-epimerase (GALE), O-glycosylation is completely eliminated and cannot be rescued by exogenous galactose or GalNAc supplementation 2. Primary hepatocytes express GALK2 to facilitate survival in glucose-depleted media containing galactose, whereas induced pluripotent stem cells, which express minimal GALK2, undergo apoptosis under these conditions 3. Beyond carbohydrate metabolism, GALK2 may have broader biological roles, as DNA methylation of GALK2 has been identified as a potential epigenetic marker for cognitive-behavioral therapy response in obsessive-compulsive disorder 4. Additionally, circular RNA derived from GALK2 (circ-GALK2) regulates vascular smooth muscle cell calcification through a miR-134-3p/CD36 axis 5.