MUTANTS OF METHYLOBACTERIUM-EXTORQUENS AND PARACOCCUS-DENITRIFICANS DEFICIENT IN C-TYPE CYTOCHROME BIOGENESIS SYNTHESIZE THE METHYLAMINE-DEHYDROGENASE POLYPEPTIDES BUT CANNOT ASSEMBLE THE TRYPTOPHAN-TRYPTOPHYLQUINONE GROUP

Five mutants of Methylobacterium extorquens and four mutants of Paraco ccus denitrificans that have a general defect in c-type cytochrome syn thesis also failed to assemble an active methylamine dehydrogenase. In all cases methanol dehydrogenase, another periplasmic enzyme, was ful ly active. All nine mutant strains accumulated both the heavy and ligh t subunits of methylamine dehydrogenase to essentially wild-type level s. In all nine mutants, the heavy-subunit and light-subunit polypeptid es were proteolytically processed, suggesting that translocation to th e periplasm had occurred, in the case of the P. denitrificans mutants, a periplasmic location for the heavy and light subunits was confirmed experimentally. While specific quinone staining of the methylamine de hydrogenase light subunit in wild-type M. extorquens and P. denitrific ans strains could readily be demonstrated, the light subunit polypepti des accumulated by the mutants did not quinone stain, indicating that the methylamine dehydrogenase prosthetic group, tryptophan tryptophylq uinone, is not assembled in the absence of functional c-type cytochrom es.