Role of hypoxanthine-guanine phosphoribosyltransferase in the metabolism of fairy chemicals in rice.

Fairy chemicals (FCs), 2-azahypoxanthine (AHX), imidazole-4-carboxamide (ICA), and 2-aza-8-oxohypoxanthine (AOH), are molecules with many diverse functions in plants. The defined biosynthetic pathway for FCs is a novel purine metabolism in which they are biosynthesized from 5-aminoimidazole-4-carboxamide. Here, we show that one of the purine salvage enzymes, hypoxanthine-guanine phosphoribosyltransferase (HGPRT), recognizes AHX and AOH as substrates. Two novel compounds, AOH ribonucleotide and its ribonucleoside which are the derivatives of AOH, were enzymatically synthesized. The structures were determined by mass spectrometry, 1D and 2D NMR spectroscopy, and X-ray single-crystal diffraction analysis. This report demonstrates the function of HGPRT and the existence of novel purine metabolism associated with the biosynthesis of FCs in rice.