Kinetic studies of the reactions of some metal reconstituted metallothioneins with the electrophilic disulfide 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB)

Rabbit liver Pt7MT, Zn7MT, Bi7MT were reconstituted and the kinetic studies of the reactions with electrophilic disulphide 5, 5'-dithiobis-(2-nitrobenzoic acid) (DTNB) were investigated to explore the possible mechanism of metals release from metallothioneins. It is revealed that the Pt7MT, Zn7MT react with DTNB biphasically, yielding a four-term rate law: Rate = k1f [MT] + k2f [DTNB][MT] + k1s [MT] + k2s [DTNB][MT]. Zn7MT reacts with disulphide DTNB more rapidly and has significantly greater observed rate constants ks, kf than Pt7MT. The kinetic data for Bi7MT indicate that the reaction is monophasic and the rate law is proved to be: Rate = k1 [MT] + k2 [DTNB][MT]. The observed pseudo-first order rate constants for above MTs are insensitive to pH value. Based on the available experimental data, the different kinetic behaviors of MTs reactions with electrophilic disulphide DTNB and a possible mechanism to release the coordinated metal ions are discussed.