Function
Catalyzes the formation of 6,7-dimethyl-8-ribityllumazine by condensation of 5-amino-6-(D-ribitylamino)uracil with 3,4-dihydroxy-2-butanone 4-phosphate. This is the penultimate step in the biosynthesis of riboflavin. Is able to use the non-natural R enantiomer of 3,4-dihydroxy-2-butanone 4-phosphate as a substrate, but with less efficiency than the natural S enantiomer. Cannot use unphosphorylated 3,4-dihydroxy-2-butanone, 3,4-dihydroxy-2-butanone 3-phosphate or diacetyl as substrates.