– 5′-Guanylic acid disodium salt (GMP-5) is a purine ribonucleoside monophosphate. L-Glutamic acid and guanosine monophosphate are biosynthesized from xanthylic acid and L-glutamine via GMP synthase [glutamine-hydrolyzing]. Guanosine triphosphate and guanosine monophosphate are biosynthesized from diguanosine tetraphosphate via bis(5′-nucleosyl)-tetraphosphatase [asymmetrical]. In humans, guanosine monophosphate is involved in the kanamycin, telithromycin, tobramycin, and erythromycin action pathways, and several metabolic disorders including AICA-ribosiduria, adenosine deaminase deficiency, adenine phosphoribosyltransferase deficiency (aprt), and 2-hydroxyglutric aciduria (D and L form) pathways. Guanosine monophosphate is also found in foods like onion-family vegetables, millet, Chinese water chestnut, and red rice, serving as a potential biomarker for the consumption of these foods.