QSOX2, also known as Quiescin Sulfhydryl Oxidase 2, is an enzyme that plays a crucial role in the oxidative folding of proteins, particularly those containing multiple disulfide bonds. Primarily found in the endoplasmic reticulum (ER) of cells, QSOX2 is vital for preserving protein structure and function by catalysing the formation of disulfide bonds between cysteine residues. This activity facilitates proper protein folding, stability, and secretion, acting as a thiol oxidase which transfers electrons from reduced cysteines to molecular oxygen.