In both cases,
NH3 and CO2 are released as byproducts. Uracil catabolism,
may be an important source of ß-alanine, a precursor
for the pantothenate moiety of coenzyme A . Since cytosine is not the substrate
of this pyrimidine reductive pathway and plants lack
cytosine deaminase, catabolism of cytosine nucleotides
may proceed via uridine.