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Biochemistry. 2007 Jul 17;46(28):8472-83. Epub 2007 Jun 20.

Thioredoxin catalyzes the denitrosation of low-molecular mass and protein S-nitrosothiols.

Author information

1
Department of Surgery, The University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.

Abstract

While most proteins have critical thiols whose oxidation affects their activity, it has been suggested that S-nitrosation and denitrosation of cellular thiols are fundamental processes similar to protein phosphorylation and dephosphorylation, respectively. However, understanding the biosynthesis and catabolism of S-nitrosothiols has proven to be difficult, in part because of the low stability of this class of metabolites. Herein, we report that thioredoxin catalyzes the denitrosation of a series of S-nitrosoamino acids and S-nitrosoproteins derived from HepG2 cells. Notably, all S-nitrosoproteins with a molecular mass of 23-30 kDa were catabolized by thioredoxin. Experimental evidence is presented which shows that both glutathione and reduced human thioredoxin denitrosate S-nitrosothioredoxin, which has been suggested to act as an anti-apoptotic factor via trans-S-nitrosation of caspase 3. In HepG2 cells, we observed that S-nitrosocysteine ethyl ester impedes the activity of caspase 3. However, a subsequent incubation of the cells in nitrosothiol-free medium resulted in reconstitution of the enzymatic activity, most likely due to endogenous denitrosation of S-nitrosocaspase 3. The latter process was markedly inhibited in thioredoxin reductase-deficient HepG2 cells, suggesting that the thioredoxin/thioredoxin reductase system tends to maintain intracellular caspase 3 in a reduced, SH state. The data obtained are discussed within the general reaction mechanisms encompassing the cellular homeostasis of S-nitrosothiols.

PMID:
17580965
DOI:
10.1021/bi700449x
[Indexed for MEDLINE]

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