The refolding of hen egg white riboflavin-binding protein: effect of protein disulphide isomerase on the reoxidation of the reduced protein.

Hen egg white riboflavin-binding protein (RfBP) contains nine disulphide bonds. Provided these remain intact, the refolding of RfBP after incubation in 6 M guanidinium chloride is highly efficient with at least 95% of the binding activity regained within 3 min. Kinetic studies indicate that this regain consists of at least two phases. When the disulphide bonds of RfBP are reduced, reoxidation using a mixture of oxidized and reduced glutathione leads to less than 5% recovery of activity. However, if protein disulphide isomerase (PDI; EC 5.3.4.1) is present during the reoxidation nearly 50% activity can be regained, suggesting that PDI may play an important role in the maturation of RfBP in vivo.