MUTANTS OF ESCHERICHIA-COLI LACKING DISULFIDE OXIDOREDUCTASES DSBA AND DSBB CANNOT SYNTHESIZE AN EXOGENOUS MONOHAEM C-TYPE CYTOCHROME EXCEPT IN THE PRESENCE OF DISULFIDE COMPOUNDS

Absence through mutation of two proteins involved in periplasmic disul phide bond formation, DsbA and DsbB, results in failure of anaerobical ly grown Escherichia coli to synthesise the hole forms of either its e ndogenous c-type cytochrome nitrite reductase or exogenous cytochrome c(550) from Paracoccus denitrificans. The synthesis of both cytochrome s can be restored to the mutants by inclusion in the growth media of c ompounds containing disulphide bonds, e.g., the oxidised form of gluta thione. The results suggest that the attachment of haem to the CXXCH m otif of a periplasmic c-type cytochrome may be preceeded by the format ion of one or more intra- or intermolecular disulphide bonds involving the cysteine residues of this motif.