The thioredoxins are common small proteins having a catalytically active disulfide group that participates in many biological reactions. Together with NADPH and related enzymes, it effectively reduces the disulfide bonds of many seed proteins and neurotoxic venoms (e.g. snakes and spiders). This structure is the oxidized form, in which two of the five cysteines are linked by a disulfide bond. There are four alpha-helices and five beta-sheets having both parallel and antiparallel orientations.
The major component of red blood cells. Transports oxygen from the lungs to body tissues. Four peptide chains, each enfolding a heme prosthetic group, assemble in the quaternary structure shown here. The four globular protein chains (A, B, C & D) can be identified by color (third button), and the heme groups enlarged (last button). Chains A (blue) and C (red)-the alpha chains- are identical, but different from Chains B (green) and D (yellow)-the beta chains. The amino acid sequences are: alpha chains: VLSPADKTNVKAAWGKVGAHAGEYGAEALERMFLSFPTTK TYFPHFDLSH beta chains: VHLTPEEKSAVTALWGKVNVDEVGGEALGRLLVVYPWTQRFFESFGDLST