5-amino-5-(4-hydroxybenzyl)-6-(D-ribitylimino)-5,6-dihydrouracil + S-adenosyl-L-methionine = 7,8-didemethyl-8-hydroxy-5-deazariboflavin + 5'-deoxyadenosine + L-methionine + NH4(+) + H(+) — reaction