Sulfhydryl oxidase (SOx) is an enzyme that catalyzes the oxidation of sulfhydryl compounds. It is present in mitochondria of certain testicular cells at specific stages of functional activation. In the mature human testis moderate SOx immunoreactivity is found in Leydig cells, and lacking in Sertoli and in peritubular cells. The Adarkspermatogonia usually contain immuno-reactive mitochondria, while in Apalespermatogonia immunoreactivity is mostly low. In stage V of spermatogenesis, Apalespermatogonia were found containing immunoreactive material. Leptotene (stages IV and V) and zygotene (stage VI) primary spermatocytes display a moderate immunoreaction. It is strongest in pachytene spermatocytes of stages I–IV, decreases in stage V, and is low during diakinesis and in secondary spermatocytes. Late spermatids usually show a stronger immunoreactivity than early spermatids. At stage V of spermatogenesis the late spermatids contain only few immunoreactive particles. Spermatozoa are free of SOx-immunoreactive mitochondria. In residual bodies small amounts of SOx-immunoreactive particles are seen. Compared to rat and hamster testis, SOx immunoreactivity of the human testis is less clearly stage-dependent and it is not confined to certain germ cell stages. As deduced from the findings in patients with spermatogenic disorders, the SOx immunoreactivity of spermatogonia in human testis seems to be of diagnostic relevanc
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