Purification and kinetic analysis of cytosolic and mitochondrial thioredoxin glutathione reductase extracted from Taenia solium cysticerci

Kinetic characterization of wild‐type and mutant human thioredoxin glutathione reductase defines its reaction and regulatory mechanisms

“…The underlying mechanism of this reversible and temporary inhibition of initial velocity has not yet been elucidated. In other TGR homologs, a hysteretic behavior occurred transiently when GSSG was used as a substrate in high concentrations [34,35,[57][58][59][60]. When testing our hTGR wt in the GR assay, a substrate inhibition at concentrations above 200 lM GSSG became evident.…”

“…In addition to mice [34], TGR has so far been described and kinetically studied in Schistosoma japonicum [36], S. mansoni [5], and T. solium [35]. In Table 3, available values are compared to our data.…”

“…The current hypotheses include, for example, S-glutathionylation at Cys88 at high GSSG concentrations leading to inhibition of enzyme activity [34,57] and a putative 'substrate inhibition' leading to longer lag periods at higher GSSG concentrations [35]. The underlying mechanism of this reversible and temporary inhibition of initial velocity has not yet been elucidated.…”

“…The current hypotheses include, for example, S-glutathionylation at Cys88 at high GSSG concentrations leading to inhibition of enzyme activity [34,57] and a putative 'substrate inhibition' leading to longer lag periods at higher GSSG concentrations [35]. Some authors explained this effect with a strong, temporary substrate inhibition of GSSG that was reversible by increasing the enzyme concentration [35], and others suggested that the lag phase depended on the Grx domain of TGR [59]. However, at none of the GSSG concentrations tested (0.1-4 mM) was a lag phase of the catalyzed reaction observed (Fig.…”

“…First described in mice [31], S. mansoni [32], and Echinococcus granulosus [33], TGR was shown to be a hybrid enzyme, providing TrxR, Grx, and even GR activity. These three proteins generally co-occur with TGR in mammals [1]; however, platyhelminths such as Schistosoma and Taenia solium lack TrxR and GR as independent entities and depend solely on TGR, which can occur in cytosolic and mitochondrial isoforms [32,[34][35][36][37]. Sun et al [38] were the first to describe hTGR in 1999; however, since then, most studies on mammalian TGR were conducted with the mouse enzyme [1, [38][39][40][41][42][43].…”