Catalyzes a salvage reaction resulting in the formation of AMP, that is energically less costly than de novo synthesis. May lack catalytic activity. AMP + diphosphate = 5-phospho-alpha-D-ribose 1-diphosphate + adenine Purine metabolism; AMP biosynthesis via salvage pathway; AMP from adenine: step 1/1. Present with 937 molecules/cell in log phase SD medium. Belongs to the purine/pyrimidine phosphoribosyltransferase family.