Properties and biological activities of thioredoxins

The mammalian thioredoxins are a family of small (approximately 12 kDa) red ox proteins that undergo NADPH-dependent reduction by thioredoxin reductase and in turn reduce oxidized cysteine groups on proteins. The two main thio redoxins are thioredoxin-l, a cytosolic and nuclear form, and thioredoxin-2 , a mitochondrial form. Thioredoxin-1 has been studied more. It performs ma ny biological actions including the supply of reducing equivalents to thior edoxin peroxidases and ribonucleotide reductase, the regulation of transcri ption factor activity, and the regulation of enzyme activity by heterodimer formation. Thioredoxin-l stimulates cell growth and is an inhibitor of apo ptosis. Thioredoxins may play a role in a variety of human diseases includi ng cancer. An increased level of thioredoxin-l is found in many human tumor s, where it is associated with aggressive tumor growth. Drugs are being dev eloped that inhibit thioredoxin and that have antitumor activity.