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 located in the endoplasmic reticulum (ER) of cells, QSOX2 is vital for preserving protein structure and function by catalyzing the formation of disulfide bonds between cysteine residues. This activity facilitates proper protein folding, stability, and secretion, functioning as a thiol oxidase that transfers electrons from reduced cysteines to molecular oxygen.