phosphoribosyltransf

One of a group of enzymes (EC 2.4.2.x, pentosyltransferases) that transfers d-ribose 5-phosphate from 5-phospho-α-d-ribosyl pyrophosphate to a purine, pyrimidine, or pyridine acceptor, forming a 5'-nucleotide and pyrophosphate, or d-ribose from d-ribosyl phosphate to a base, forming a nucleoside, or similar pentose transfers; important in nucleotide biosynthesis. Specific phosphoribosyltransferases are preceded by the name of the acceptor base, for example, uracil phosphoribosyltransferase (that is, uracil + PRPP ⇋ UMP + pyrophosphate).