The purines are a group of molecules that are naturally found in all living things. They are involved in a great number of biochemical pathways that are essential for life. They provide the basic building blocks for DNA and RNA. ATP is a purine that serves as the currency of the majority of energy-requiring reactions in cells. The cyclic nucleotides and other purines such as adenosine serve as messenger molecules for cellular communication.

Because of the importance of purines for so many basic biological processes, their amounts are very tightly regulated. Cellular purines derive from two major sources. They can be made from other molecules in series of steps known as the de novo synthetic pathway, or they can be regenerated from bases hypoxanthine and guanine. This last pathway, recycling of hypoxanthine and guanine, is the reaction mediated by HPRT.