ABSTRACT
A protein similar to Ahp C has been found in yeast as a thiol-spe cific antioxidant protein that protects enzyme proteins against thiol-
dependent metal catalyzed oxidation (4). This protein catalyzes reduc tion of H20 2 and alkyl hydroperoxides with the use of electrons pro vided by thioredoxin (5). Therefore, this protein can be called thioredoxin peroxidase (TPx). More than thirty proteins have been shown to have sequence homology to Ahp C and TPx proteins so far (see Chap. 7). These proteins have one or two highly conserved regions contain ing cysteine residue, presumably an active center in the function. In mammalian cells, more than ten proteins have the homology to the yeast TPx. Interestingly, they were found as the proteins possessing the dif ferent functions; from red blood cells as the natural killer-enhancing factor (NKEF) (6); from mouse erythroleukemia cells as the protein observed when the cells differentiate to erythrocytes (MER 5) (7); from the mitochondrial matrix of bovine adrenal cortex as one of the sub strates for the ATP-dependent protease (SP-22) (8); from rat hepatocytes and hepatoma cells as the heme-binding protein (HBP23) (9); and from human mammary epithelial cell line as proliferation associated gene product (PAG) (10). These proteins are recently designated as peroxiredoxin. Some of them are demonstrated to have the thiol spe cific antioxidant activity.
