The present invention generally relates to a nicotinamide adenine dinucleotide (NAD) biosynthesis system and methods of screening for NAD biosynthesis effectors. Among the various aspects of the present invention is the provision of an in vitro-reconstituted mammalian NAD biosynthesis system that can be used for the high-throughput screening of chemical activators and inhibitors for mammalian NAD biosynthesis. Another aspect of the invention provides a method of identifying a compound that effects in vivo activity of NAD metabolic enzymes. Further aspects of the invention include nucleic acid sequences, vectors, and transformed cells that can be used in the methods described herein.