Uridine-cytidine kinase (UCK) (EC 2.7.1.48) is a pyrimidine ribonucleoside kinase that catalyzes the phosphorylation of uridine and cytidine to UMP and CMP.
To understand where the uric acid comes from, let's start with purines, which, together with pyrimidines, are nature's most common nitrogen-containing heterocycles.