Protein disulfide isomerase

Protein disulfide isomerase or PDI (EC 5.3.4.1) is an enzyme in the endoplasmic reticulum that catylses the formation and breakage of disulfide bonds between cysteine residues within proteins as they fold. This allows proteins to quickly find the the correct arrangement of disulfide bonds in their fully folded state and therefore the enzyme acts to catalyse protein folding.