Distribution and possible novel role of phospholipid hydroperoxide glutathione peroxidase in rat epididymal spermatozoa.

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