Engineering of an intersubunit disulphide bridge in glutathione reductase from Escherichia coli

By site-directed mutagenesis, Thr-75 was converted to Cys-75 in the glutathione reductase (EC 1.6.4.2) of Escherichia coli. This led to the spontaneous formation of an intersubunit disulphide bridge across the 2-fold axis of the dimeric enzyme. The disulphide bridge had no deleterious effect on the catalytic activity, but nor did it increase the thermal stability of the enzyme, possibly because of local conformational flexibility on the dimer interface. The T75C mutant, like the wild-type enzyme, was inactivated by NADPH, proving that this inactivation cannot be due to simple dissociation of the dimer.