FIG. 7.

Model for Moco biosynthesis in R. capsulatus. Moco biosynthesis in R. capsulatus is predicted to proceed in a manner similar to that of Moco biosynthesis in E. coli. The molybdopterin molecule, still lacking molybdenum, is synthesized by the gene products of moaABC, moaDE, and moeB (30). For the biosynthesis of the MPT cofactor, MoeA is involved in molybdenum insertion into MPT. The role of MogA for MPT biosynthesis in R. capsulatus is yet unknown. XdhC is required to insert the MPT cofactor into XDH (21). In contrast, the biosynthesis of the MGD cofactor requires additional proteins. MogA is probably involved in molybdenum insertion, whereas MoeA is essential for MGD biosynthesis; the addition of the guanosine dinucleotide to MPT is catalyzed by MobA, the MGD synthase in R. capsulatus (22).