MeSH note : a 52 kDa protein; a growth factor for early B-LYMPHOCYTES; later identified to be
nicotinamide phosphoribosyltransferase, an enzyme that catalyzes the condensation
of nicotinamide with 5-phosphoribosyl-1-pyrophosphate yielding nicotinamide mononucleotide,
the rate limiting step in the biosynthesis of coenzyme NAD;