Protein disulphide bonds are formed in the endoplasmic reticulum of eukaryotic cells and
the periplasmic space of prokaryotic cells. The main pathways that catalyse the formation of
protein disulphide bonds in prokaryotes and eukaryotes are remarkably similar, and they
share several mechanistic features. The recent identification of new redox-active proteins in
humans and yeast that mechanistically parallel the more established redox-active enzymes
indicates that there might be further uncharacterized redox pathways throughout the cell.