:Spermosin

{{Infobox enzyme

| Name = Spermosin

| EC_number = 3.4.21.99

| CAS_number = 89925-67-7

| GO_code =

| image =

| width =

| caption =

}}

Spermosin ({{EC number|3.4.21.99}}) is an enzyme.{{cite journal | vauthors = Sawada H, Yokosawa H, Ishii S | 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 | journal = The Journal of Biological Chemistry | volume = 259 | issue = 5 | pages = 2900–4 | date = March 1984 | pmid = 6365918 }}{{cite journal | vauthors = Sawada H, Yokosawa H, Someno T, Saino T, Ishii S | 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 | journal = Developmental Biology | volume = 105 | issue = 1 | pages = 246–9 | date = September 1984 | pmid = 6381175 | doi = 10.1016/0012-1606(84)90281-1 }}{{cite journal | vauthors = Sawada H, Iwasaki K, Kihara-Negishi F, Ariga H, Yokosawa H | title = Localization, expression, and the role in fertilization of spermosin, an ascidian sperm trypsin-like protease | journal = Biochemical and Biophysical Research Communications | volume = 222 | issue = 2 | pages = 499–504 | date = May 1996 | pmid = 8670234 | doi = 10.1006/bbrc.1996.0773 }}{{cite journal | vauthors = Sawada H, Someno T | title = Substrate specificity of ascidian sperm trypsin-like proteases, spermosin and acrosin | journal = Molecular Reproduction and Development | volume = 45 | issue = 2 | pages = 240–3 | date = October 1996 | pmid = 8914083 | doi = 10.1002/(SICI)1098-2795(199610)45:2<240::AID-MRD18>3.0.CO;2-4 }} This enzyme catalyses the following chemical reaction

: Hydrolyses arginyl bonds, preferably with Pro in the P2 position

This enzyme is isolated from the ascidian (Prochordate) Halocynthia roretzi.