DISTRIBUTION AND POSSIBLE NOVEL ROLE OF PHOSPHOLIPID HYDROPEROXIDE GLUTATHIONE-PEROXIDASE IN RAT EPIDIDYMAL SPERMATOZOA

The selenoenzyme phospholipid hydroperoxide glutathione peroxidase (PH GPx, EC 1.11.1.12) is present, in both free and membrane-bound form, i n several mammalian tissues. It utilizes thiols such as glutathione to specifically scavenge phospholipid hydroperoxides. The testis exhibit s the highest PHGPx-specific activity so far measured, and interest in the presence and function of the enzyme in this tissue has recently g rown. Here we report the localization of PHGPx in rat epididymal sperm atozoa and its distribution in subfractions obtained by sucrose densit y gradient centrifugation. Immunochemical evidence and enzymatic activ ity revealed for the first time that PHGPx is present in sperm heads a nd tail midpiece mitochondria. The binding of the enzyme to spermatozo a, head, and mitochondria was barely affected by ionic strength or thi ols or detergents, as compared to the detachment of PHGPx obtained fro m testis nuclei. Moreover, we demonstrated that pure PHGPx exhibits a higher thiol-oxidase activity toward isolated epididymal caput protami nes than toward protamines from epididymal cauda. These results sugges t a role for the enzyme in the maturation of spermatozoa through the m etabolism of hydroperoxides and sperm thiol oxidation, in addition to its serving as an antioxidant protector.