Single-molecule dynamics of conformational changes in flavin adenine dinucleotide

Dynamic conformational changes of the prosthetic group, flavin adenine dinucleotide (FAD), in flavoprotein NADH peroxidase (Npx), in thioredoxin reductase (TrxR), and in free solution were monitored with total internal reflection fluorescence microscopy. FAD bound loosely in the proteins changed from the stacked conformation to the unstacked conformation upon laser excitation. On the other hand, our results show that FAD in free solution not only underwent conformational changes but also reacted with each other to form a dimer.