Like the discoveries of nicotinic acid by Conrad Elvehjem and Priess and Handler, Brenner and colleagues first identified a new precursor or building block of NAD and then the enzymes that are used to convert that precursor to NAD. This work uncovered a two step pathway by which nicotinamide riboside in converted to NAD and later work showed that feeding nicotinamide riboside to cells resulted in increased NAD levels and extended lifespan in yeast. http://linkinghub.elsevier.com/retrieve/pii/S0092867404004167 and https://www.ncbi.nlm.nih.gov/pubmed/17482543