Assays of Thiol Isomerase Enzymatic Activity.

Thiol isomerases are oxidoreductases that mediate disulphide bond formation in nascent proteins of the endoplasmic reticulum to ensure their structural integrity. In addition to its role in protein folding, thiol isomerases can modify allosteric disulphide bonds in both intracellular and extracellular proteins, thereby controlling protein function. The process of disulphide bond formation and cleavage is strictly regulated and responsive to redox conditions. Understanding disulphide bond regulation under different redox environments is critical to understanding physiological and pathological processes related to disulphide bond chemistry. Here we describe protocols for the measurement of disulphide bond modulation by thiol isomerases, including reductase and denitrosylase assays. These methods can be applied to study recombinant thiol isomerases and thiol isomerases in cellular settings.