Identification and characterization of superoxide dismutase in silkworm seminal fluid

Long-term exposure of human sperm cells to reactive oxygen species (ROS) can cause decreased motility and viability, as well as DNA fragmentation. An antioxidant defense system, called a preventive antioxidant system, is therefore needed to maintain low ROS concentrations in sperm and seminal plasma. Superoxide dismutase (SOD, EC 1.15.1. 1), one of the most important antioxidant enzymes, catalyzes the conversion of superoxide radical (O2•−) to hydrogen peroxide (H2O2) and molecular oxygen (O2). In this report, we documented a high SOD activity level in the reproductive organs of the male silkmoth (Bombyx mori, L.), particularly in the glandula lacteola, and found that about 90% of the SOD activity was transferred to females by ejaculation and maintained. We characterized three cDNAs from the adult male reproductive system: a soluble cytoplasmic copper/zinc SOD (Cu/Zn SOD, SOD1) and two extracellular forms of copper/zinc SOD (EC-SOD, SOD3). The levels of transcription and protein accumulation of Bombyx SOD1 indicated that it is abundantly present in the extracellular fluid of the male glandula lacteola, which transfers to the female during ejaculation. Furthermore, it was observed that some of the transferred SOD1 exists in the sperm fraction stored in the mating female’s bursa copulatrix. Our present results demonstrate the origins of seminal SOD activities and suggest that SOD might be a potential source and function of antioxidants in semen and also may control the amount of extracellular ROS involved in sperm quality maintenance.