Mitochondrial Thioredoxin-Glutathione Reductase from LarvalTaenia crassiceps(Cysticerci)

Abstract

Mitochondrial thioredoxin-glutathione reductase was purified from larval Taenia crassiceps (cysticerci). The preparation showed NADPH-dependent reductase activity with either thioredoxin or GSSG, and was able to perform thiol/disulfide exchange reactions. At 25°C specific activities were 437 ± 27 mU mg−1 and 840 ± 49 mU mg−1 with thioredoxin and GSSG, respectively. Apparent Km values were 0.87 ± 0.04 μM, 41 ± 6 μM and 19 ± 10 μM for thioredoxin, GSSG and NADPH, respectively. Thioredoxin from eukaryotic sources was accepted as substrate. The enzyme reduced H2O2 in a NADPH-dependent manner, although with low catalytic efficiency. In the presence of thioredoxin, mitochondrial TGR showed a thioredoxin peroxidase-like activity. All disulfide reductase activities were inhibited by auranofin, suggesting mTGR is dependent on selenocysteine. The reductase activity with GSSG showed a higher dependence on temperature as compared with the DTNB reductase activity. The variation of the GSSG- and DTNB reductase activities on pH was dependent on the disulfide substrate. Like the cytosolic isoform, mTGR showed a hysteretic kinetic behavior at moderate or high GSSG concentrations, but it was less sensitive to calcium. The enzyme was able to protect glutamine synthetase from oxidative inactivation, suggesting that mTGR is competent to contend with oxidative stress.

Inhibition of thioredoxin reductase by lanthanum chloride

“…Recently, a similar behaviour was found also with thioredoxinglutathione reductase (TGR) isolated from the larval Taenia crassiceps (cysticerci) [10]. The cytosolic isoform of TGR shows a noticeably higher sensitivity to calcium ion inhibition in comparison to the corresponding mitochondrial isoform [10]. Taking into account the strict similarity between calcium and lanthanum ions, we have studied the effects of LaCl 3 on TrxR, in order to make a comparison with the results previously obtained on TrxR treated with calcium ions, especially considering the differential and contrasting inhibitory effects observed with this cation [1][2][3][4][5][6][7][8].…”

“…However, while the cytosolic isoform of this enzyme (TrxR1) is markedly inhibited by calcium ions, the corresponding mitochondrial enzyme (TrxR2) is far less affected [5]. Recently, a similar behaviour was found also with thioredoxinglutathione reductase (TGR) isolated from the larval Taenia crassiceps (cysticerci) [10]. The cytosolic isoform of TGR shows a noticeably higher sensitivity to calcium ion inhibition in comparison to the corresponding mitochondrial isoform [10].…”

Low-Molecular-Mass Antioxidants in Parasites

“…As mammalian TrxRs, TGRs are selenoproteins with a C-terminal Gly-Cys-SeCys-Gly motif. The parasite TGR occurs in the cytosol and mitochondria of the worms (2,28,92). It is essential for Schistosoma survival and is currently investigated as a target for specific antischistosomal chemotherapy (137).…”

Auranofin-induced oxidative stress causes redistribution of the glutathione pool in Taenia crassiceps cysticerci

“…To date, TGR has been reported in the trematodes Schistosoma mansoni [26], Fasciola hepatica [27] and S. japonicum [28], as well as in the cestodes Echinococcus granulosus [29] and Taenia crassiceps [30]. Subsequent studies showed that in flatworms cytosolic and mitochondrial isoforms are encoded by a single gen [31] although with different kinetic properties [32].…”