Since Conrad Elvehjem showed that nicotinic acid was the agent that prevented pellagra and Arthur Kornberg had shown the reaction by which NAD was made in the cell, Jack Priess and Philip Handler did work to uncover how nicotinic acid was converted to NAD. In their work, they showed that nicotinic acid is converted in three steps to NAD, and the identified the protein/enzymes responsible for these steps. Today we refer to the “pathway” by which nicotinic acid is converted to NAD as the Priess-Handler pathway. http://www.jbc.org/content/233/2/488.full.pdf+html and https://www.ncbi.nlm.nih.gov/pubmed/13563527