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