Cofactors play key roles in metabolic pathways. Among them F-420 has proved to be a very attractive target for the selective inhibition of archaea and actinobacteria. Its biosynthesis, in a unique manner, involves a key enzyme, F-0-synthase. This enzyme is a large monomer in actinobacteria, while it is constituted of two subunits in archaea and cyanobacteria. We report here the purification of both types of F-0-synthase and their in vitro activities. Our study allows us to establish that F-0-synthase, from both types, uses 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione and tyrosine as substrates but not 4-hydroxylphenylpyruvate as previously suggested. Furthermore, our data support the fact that F-0-synthase generates two 5'-deoxyadenosyl radicals for catalysis which is unprecedented in reaction catalyzed by radical SAM enzymes.