Catalyzes the transfer of the gamma-phosphate of ATP to D-galactose to form alpha-D-galactose-1-phosphate (Gal-1-P). Is very specific for its substrate, since it is not able to use D-glucose, D-fructose, D-mannose, 2-deoxy-D-glucose, and D-glucosamine as substrates. alpha-D-galactose + ATP = ADP + alpha-D-galactose 1-phosphate + H(+) Optimum pH is 5.0. Optimum temperature is 90 degrees Celsius. Carbohydrate metabolism; galactose metabolism. Monomer. Belongs to the GHMP kinase family. GalK subfamily.