Specific thiol compounds complement deficiency in c-type cytochrome biogenesis in Escherichia coli carrying a mutation in a membrane-bound disulphide isomerase-like protein.

Escherichia coli JCB606 carries a mutation in the dipZ gene, known to code for a disulphide isomerase-like protein, with the consequence that holo forms of neither exogenous nor endogenous c-type cytochromes are synthesised. This failure has been overcome by adding compounds containing thiol groups to the growth medium. Only L-cysteine and 2-mercaptoethane sulphonic acid were effective, suggesting a (stereo)specific binding site that could be occupied by these compounds in the absence of the catalytic domain of DipZ.