pro·ta·mine 
(prōtə-mēn′, -mĭn) also pro·ta·min (-mĭn)
(prōtə-mēn′, -mĭn) also pro·ta·min (-mĭn)n.
Any of a group of arginine-rich proteins that bind to and package DNA in the sperm nucleus. Protamines are used in long-acting formulations of insulin and to neutralize the anticoagulant effects of heparin.