Abstract: Methods and prokaryotic expression systems for producing recombinant disulfide bond-containing proteins are described including increasing the level of at least one redox cofactor in the cell to enhance disulfide bond formation are disclosed. Processes of increasing levels of redox cofactors include media supplementation and genetic modification of the host cell. The process can yield increased levels of soluble or active protein, or can assist the proper processing of recombinant proteins in expression systems.