Differential effect of calcium ions on the cytosolic and mitochondrial thioredoxin reductase.
The effect of calcium ions has been studied on three different isoforms of thioredoxin reductase. The cytosolic (TrxR1), mitochondrial (TrxR2), and the Escherichia coli enzymes were examined and compared. In our condition, TrxR1 appears extremely sensitive to Ca2+ showing an IC50 of about 160 nM, while Ca2+ exerts only a weak inhibitory effect on the mitochondrial isoform. The thioredoxin reductase purified from E. coli is almost completely insensitive to calcium ions. Circular dichroism analysis of highly purified mitochondrial and cytosolic thioredoxin reductases reveals that Ca2+ induces conformational alterations that are particularly relevant only in the cytosolic isoform. These observations are discussed with reference to the physiological role and, in particular, to the regulatory functions of the thioredoxin system.
Dipartimento di Chimica Biologica, Università di Padova, Viale G. Colombo 3, 35121 Padova, Italy.
Maria Pia
MP
Rigobello
Fabio
F
Vianello
Alessandra
A
Folda
Chiara
C
Roman
Guido
G
Scutari
Alberto
A
Bindoli
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002412:Cations; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology*; D004533:Egtazic Acid / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D054481:Thioredoxin Reductase 1; D054482:Thioredoxin Reductase 2; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism*
D002412:Cations; D002614:Chelating Agents; D004533:Egtazic Acid; D054481:Thioredoxin Reductase 1; D054482:Thioredoxin Reductase 2; D013880:Thioredoxin-Disulfide Reductase; C516126:Txnrd1 protein, rat; C516129:Txnrd2 protein, rat; D002118:Calcium