Identification of parvalbumin-like protein as a major protein of common carp (Cyprinus carpio L) spermatozoa which appears during final stage of spermatogenesis.

Parvalbumin is well known as the major fish allergen that is typically present in high amounts in muscles, where it functions in calcium buffering and is involved in the relaxation process in fast-twitch muscles. We show in our current study that parvalbumin-like protein is present in high amounts in carp spermatozoa. It is the first report to demonstrate the presence of parvalbumin-like protein in fish spermatozoa. Using antibodies produced against purified carp parvalbumin-like protein, we localized parvalbumin-like protein to spermatids and spermatozoa. Our results indicate that parvalbumin-like protein appeared during the final stage of spermatogenesis. We also detected high amounts of parvalbumin-like protein in carp seminal plasma but not in blood plasma which suggests that its function may be specific for the male reproductive tract. The activation mechanism of carp sperm movement is not fully understood, but in carp, Ca2+ influx is the prerequisite for the initiation of sperm motility. The appearance of parvalbumin-like protein in high amounts in mature spermatozoa coincides with their acquiring the ability to move. The presence of parvalbumin-like protein in spermatozoa and seminal plasma strongly suggests that parvalbumin-like protein is an important part of the Ca2+-mediated mechanism of sperm activation in carp.