... 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone5¢-phosphate (Compound 4, Fig. 1), is the first committedprecursor in the biosynthesis of riboflavin (vitamin B2)[5].Recently, GTP cyclohydrolase II was also shown to catalyzethe formation of GMP ... centralmetabolic pathways that are crucial for energy transduction.The precursor of flavocoenzymes, riboflavin (vitamin B2), isFig. 3. Ultraviolet spectra. A reaction mixture containing 100 mMTris/HCl,pH8.0,10mMMgCl2,90lMGTP,...