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. Homodimer. Highly expressed in the insect stage (Promastigote). Belongs to the AdoMet synthase family.