Ripe unfertilized eggs of the Pacific herring, Clupea pallasii, release sperm-activating proteins into seawater at the time of fertilization. Five species of herring sperm-activating proteins (HSAP) with different pl values (4.8, 4.9, 5.0, 5.1 and 5.4) were purified from the egg-conditioned medium by gel filtration and isoelectric focusing. Molecular mass of the HSAP (pl = 5.1), the major species of the five HSAP, was determined to be 8.1 kDa by mass spectrometry. Molecular weights of all of the HSAP were estimated to be 7700 by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The first 20 amino acid sequences from N-terminal ends of three HSAP (pl = 4.9, 5.0 and 5.1) were almost identical, suggesting that the HSAP have similar structures.
Keywords: herring sperm activation; immobilized pH gradient-isoelectric focusing; sperm-activating protein.