GTP cyclohydrolase II catalyses the first committed step in the biosynthesis of riboflavin.

1: Biosynthesis of riboflavin: cloning, sequencing, mapping, and expression of the gene coding for GTP cyclohydrolase II in Escherichia coli. Richter G, Ritz H, Katzenmeier G, Volk R, Kohnle A, Lottspeich F, Allendorf D, Bacher A; J Bacteriol 1993;175:4045-4051. PMID:8320220