Does not seem to have NDK kinase activity. Confers protection from cell death by Bax and alters the cellular levels of several antioxidant enzymes including Gpx5. May play a role in spermiogenesis by increasing the ability of late-stage spermatids to eliminate reactive oxygen species. Additional isoforms seem to exist. Expressed in the trachea, ependymal cells and oviduct (at protein level) (PubMed:32203505). Expressed predominantly in germ cells of the testis. Not expressed in testicular somatic cells. First appears in pachytene spermatocytes and increases in abundance in subsequent stages. Belongs to the NDK family.