Acts on GalNAc. Also acts as a galactokinase when galactose is present at high concentrations. May be involved in a salvage pathway for the reutilization of free GalNAc derived from the degradation of complex carbohydrates. ATP + N-acetyl-alpha-D-galactosamine = ADP + H(+) + N-acetyl-alpha-D-galactosamine 1-phosphate Monomer. Belongs to the GHMP kinase family. GalK subfamily.