The esterolytic activity of epidermolytic toxins

The two epidermolytic toxins were shown to have intrinsic N-t-butyloxycarbonyl-L-glutamic acid alpha-phenyl esterase activity. The activity was dependent on free toxin pKa values of 6.6 and 6.8 for ETA and ETB respectively. ETB incorporated 0.97 mol of radiolabelled di-isopropyl phosphorofluoridate/mol of protein with loss of esterolytic and epidermolytic activities. The correspondence of epidermolytic and esterolytic activities in ETA and ETB during thermal inactivation and reaction with di-isopropyl phosphorofluoridate, together with the inactivity of the mutant protein ETA S195G, demonstrates that the two activities are dependent on a single active serine residue in each protein.