Substrate-level phosphorylation is a type of metabolism that results in the formation and creation of Adenosine Triphosphate (ATP) or Guanosine Triphosphate (GTP) by the direct transfer and donation of a phosphoryl (P03) group to Adenosine Diphosphate (ADP) or Guanosine Diphosphate (GDP) to form a phosphorylated reactive intermediate.