Notes: Thymine is a pyrimidine base.{58925} It forms complementary base pairs with the purine adenine (Item No. 18148) in DNA.{58925} Thymine is produced by the catabolism of thymidine (Item No. 20519) via thymidine phosphorylase.{58926} It is replaced with uracil (Item No. 26088) in RNA.{58927}