Purification and characterization of glutathione peroxidase from human blood platelets. Age-related changes in the enzyme.

Platelet glutathione peroxidase (GPx) is known to play a pivotal role in controlling the level of lipid hydroperoxides, especially those resulting from the 12-lipoxygenase activity. GPx was purified from the cell cytosol by more than 700-fold using an exchange chromatography, FPLP, gel filtration and covalent fixation. Isoelectric focusing revealed a peak activity at pH 5.1. The molecular mass of the enzyme was found between 90 and 100 kDa by gel filtration, and was approximating at 23 kDa by SDS-PAGE. A polyclonal antibody raised against commercial bovine erythrocyte GPx recognized the human platelet enzyme. It is concluded that human platelet GPx is likely a homotetramer of 92 kDa as described for most other sources. We have also found that the decreased platelet GPx activity observed in platelets from elderly people is associated with a lower content of the immunoreactive enzyme.