Kinetics of inhibition of aminoacylase activity by dithiothreitol or 2-mercaptoethanol.

The previously described kinetic method of the substrate reaction during irreversible inhibition of enzyme activity [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381-436] has been used to study the inactivation kinetics of aminoacylase by dithiothreitol (DTT) and 2-mercaptoethanol (MET). The results show that the inactivation of aminoacylase by DTT or MET is competitive slow-reversible inhibition. The microscopic rate constants for the inactivation reaction were determined. Removal of these inhibitors by dialysis can lead to complete recovery of enzymatic activity. The present results also show that the presence of equimolar Zn2+ to DTT gives complete protection of the enzyme against the inactivation by DTT. Moreover, addition of equimolar amounts of Zn2+ to DTT can induce recovery of the enzymatic activity of DTT-inactivated enzyme. It is known that aminoacylase from pig kidney contains no disulfide bonds. Therefore, it may be suggested that inactivation of aminoacylase by dithiothreitol or 2-mercaptoethanol is not due to the reduction of disulfide bonds, and is a competitive slow-reversible inhibition.