Microbial metabolism of quinoline and related compounds. X. The molybdopterin cofactors of quinoline oxidoreductases from Pseudomonas putida 86 and Rhodococcus spec. B1 and of xanthine dehydrogenase from Pseudomonas putida 86.

The bis(carboxamidomethyl) derivatives of the molybdenum cofactors in three eubacterial molybdo-iron/sulphur-flavoproteins were examined. The quinoline oxidoreductases from Pseudomonas putida 86 and Rhodococcus spec. B1 contain molybdopterin cytosine dinucleotide. In xanthine dehydrogenase from Pseudomonas putida 86, however, only molybdopterin was found. The bis(carboxamidomethyl) derivatives of all three enzymes were treated with nucleotide pyrophosphatase, but only those of the quinoline oxidoreductases were cleaved into [bis(carboxamidomethyl)]molybdopterin and CMP, whereas that of xanthine dehydrogenase remained unchanged. Dephosphorylation by alkaline phosphatase yielded dephospho-[bis(carboxamidomethyl)]molybdopterin and cytidine from the cleaved molybdopterin cytosine dinucleotide. The bis(carboxamidomethyl) derivative from xanthine dehydrogenase was converted to dephospho-[bis(carboxamidomethyl)]molybdopterin by alkaline phosphatase. Acid hydrolysis of the purified enzymes and analysis of the hydrolysate by HPLC confirmed that compared with the xanthine dehydrogenase both quinoline oxidoreductases contain CMP.