Catalyzes the formation of S-adenosylmethionine from methionine and ATP. The reaction comprises two steps that are both catalyzed by the same enzyme: formation of S-adenosylmethionine (AdoMet) and triphosphate, and subsequent hydrolysis of the triphosphate. ATP + H2O + L-methionine = diphosphate + phosphate + S-adenosyl-L-methionine Binds 2 magnesium ions per subunit. The magnesium ions interact primarily with the substrate. Binds 1 potassium ion per subunit. The potassium ion interacts primarily with the substrate. Amino-acid biosynthesis; S-adenosyl-L-methionine biosynthesis; S-adenosyl-L-methionine from L-methionine: step 1/1. Heterotetramer. In yeast, there are two genes coding for AdoMet synthase. Present with 22000 molecules/cell in log phase SD medium. Belongs to the AdoMet synthase family.