Function[edit]
Thioredoxins are proteins that act as antioxidants by facilitating the reduction of other proteins by cysteine thiol-disulfide exchange. Thioredoxins are found in nearly all known organisms and are essential for life in mammals.[3][4]
Thioredoxin is a 12-kD oxidoreductase enzyme containing a dithiol-disulfide active site. It is ubiquitous and found in many organisms from plants and bacteria to mammals. Multiple in vitro substrates for thioredoxin have been identified, including
ribonuclease, choriogonadotropins, coagulation factors, glucocorticoid receptor, and insulin. Reduction of insulin is classically used as an activity test.
[5]
Thioredoxins are characterized at the level of their
amino acid sequence by the presence of two
vicinal cysteines in a CXXC
motif. These two cysteines are the key to the ability of thioredoxin to reduce other proteins. Thioredoxin proteins also have a characteristic
tertiary structure termed the
thioredoxin fold.
The thioredoxins are kept in the reduced state by the flavoenzyme
thioredoxin reductase, in a NADPH-dependent reaction.
[6] Thioredoxins act as electron donors to
peroxidases and
ribonucleotide reductase.
[7] The related
glutaredoxins share many of the functions of thioredoxins, but are reduced by
glutathione rather than a specific reductase.
The benefit of thioredoxins to reduce oxidative stress is shown by transgenic mice that overexpress thioredoxin, are more resistant to inflammation, and live 35% longer[8] — supporting thefree radical theory of aging. However, the controls of this study were short lived, which may have contributed to the apparent increase in longevity.[9]
Plants have an unusually complex complement of Trxs composed of six well-defined types (Trxs f, m, x, y, h, and o) that reside in different
cell compartments and function in an array of processes. In 2010 it was discovered for the first time that thioredoxin proteins are able to move from
cell to cell, representing a novel form of cellular communication in plants.
[2]
