Identification of the First Human Glutaredoxin Pseudogene Localized to Human Chromosome 20qll.2

Abstract

Thiol-disulfide interchange reactions are one of the most important regulatory systems in cells. Two kinds of molecules are responsible for this process: non-protein low molecular weight thiols and thiol-containing proteins of higher molecular weight (Zlieger, 1985). Among the first type, glutathione arises as the most important reductant in cell, while thioredoxin (Trx), glutaredoxin (Grx) and protein disulfide isomer-ase (PDI) are the best known examples of regulatory proteins by thiol-disulfide interchange reactions (Holmgren, 1989). Thioredoxins and glutaredoxins share many common features like being small, heat-stable, globular proteins (around 12 kDa), with a similar tridimensional structure (thioredoxin fold) and both using NADPH as source of reducing equivalents (Holmgren, 1989). However, while the electron from NADPH is transferred to the flavoenzyme thioredoxin reductase that in turn reduces thioredoxin (the so-called thioredoxin system), glutaredoxin is reduced by the sequential transfer of reducing power from NADPH to glutathione reductase and glutathione (the so-called glutaredoxin system) (Holmgren, 1989). Once reduced, Trx and Grx can act as general disulfide oxidoreductases with preference shown by Trx for peptide substrates while Grx shows preference for low-molecular weight dithiol- containing molecules (Holmgren, 1989). Grx was initially discovered as an alternative hydrogen donor for the essential enzyme ribonucleotide reductase in a thioredoxin-deficient mutant of E. coli (Holmgren, 1976; Holmgren, 1979). Since then Grx has also been shown to be an electron donor for enzymes like adenosine 3′-phos- phate-5′-phosphosulfate reductase and methionine sulfoxide reductase, functions that Trx also displays (Holmgren, 1989). In addition, Grx has been implicated in deiodination of thyroxine to triiodothyronine and has shown dehydroascor- bate reductase activity that generates ascorbic acid which protects neutrophils against the deleterious effects of the respiratory burst (Goswami and Rosenberg, 1985; Park and Levine, 1996).