1. ^{{cite journal | title = Purification and characterization of two types of trypsin-like enzymes from sperm of the ascidian (Prochordata) Halocynthia roretzi. Evidence for the presence of spermosin, a novel acrosin-like enzyme |author1 = Sawada, H. |author2 =Yokosawa, H. |author3 =Ishii, S. |journal = J. Biol. Chem. |date = 1984 |volume = 259 |pages = 2900-2904 |pmid = 6365918}}
2. ^{{cite journal | title = Evidence for the participation of two sperm proteases, spermosin and acrosin, in fertilization of the ascidian, Halocynthia roretzi: inhibitory effects of leupeptin analogs on enzyme activities and fertilization |author1 = Sawada, H. |author2 =Yokosawa, H. |author3 =Someno, T. |author4 =Saino, T. |author5 =Ishii, S. |journal = Dev. Biol. |date = 1984 |volume = 105 |pages = 246-249 |pmid = 6381175 |doi=10.1016/0012-1606(84)90281-1}}
3. ^{{cite journal | title = Localization, expression, and the role in fertilization of spermosin, an ascidian sperm trypsin-like protease |author1 = Sawada, H. |author2 =Iwasaki, K. |author3 =Kihara-Negishi, F. |author4 =Ariga, H. |author5 =Yokosawa, H. |journal = Biochem. Biophys. Res. Commun. |date = 1996 |volume = 222 |pages = 499-504 |pmid = 8670234 |doi=10.1006/bbrc.1996.0773}}
4. ^{{cite journal | title = Substrate specificity of ascidian sperm trypsin-like proteases, spermosin and acrosin |author1 = Sawada, H. |author2 =Someno, T. |journal = Mol. Reprod. Dev. |date = 1996 |volume = 45 |pages = 240-243 |pmid = 8914083 |doi=10.1002/(SICI)1098-2795(199610)45:2<240::AID-MRD18>3.0.CO;2-4}}