Notes: Cytidine-d2 is intended for use as an internal standard for the quantification of cytidine (Item No. 29602) by GC- or LC-MS. Cytidine is a pyrimidine nucleoside composed of ribose and a cytosine base.{48688} It forms complementary base pairs with the purine nucleoside guanosine (Item No. 27702) in DNA and RNA. Cytidine is a precursor of uridine (Item No. 20300) and can also be phosphorylated by uridine-cytidine kinase to form cytidine 5'-monophosphate (CMP; Item No. 35116).{31864,48688} It rescues inhibition of proliferation induced by knockdown of CTP synthase 1 in T cells when used at a concentration of 200 µM.{26255}