May bind to phospholipids. May act as serine protease inhibitor (By similarity). At the cell periphery in pachytene spermatocytes and round spermatids, in the distal dorsal region of the sperm head and in the sperm tail. Testis specific. First detected 14 day old testes, with the first appearance of stage IX pachytene spermatocytes. Highly expressed in stage X and XI pachytene and diplotene spermatocytes from day 18 to 22. Belongs to the phosphatidylethanolamine-binding protein family.