Protamines are small, arginine-rich, nuclear proteins that replace histones late in the haploid phase of spermatogenesis and are believed essential for sperm head condensation and DNA stabilization. They may allow for denser packaging of DNA in spermatozoon than histones, but they must be decompressed before the genetic data can be used for protein synthesis. However, in humans and maybe other primates, 10-15% of the sperm's genome is packaged by histones thought to bind genes that are essential for early embryonic development.
Medical uses 
When mixed with insulin, protamines slow down the onset and increase the duration of insulin action (see NPH insulin).
Protamine is used in cardiopulmonary bypass surgery to neutralize the anti-clotting effects of heparin. Adverse effects include increased pulmonary artery pressure and decrease peripheral blood pressure, myocardial oxygen consumption, cardiac output, and heart rate.
Protamine sulfate is an antidote for heparin overdose. A chain shortened version of protamine also acts as a potent heparin antagonist, but with markedly reduced antigenicity.
In gene therapy, protamine sulfate's ability to condense plasmid DNA along with its approval by the U.S. Food and Drug Administration (FDA) have made it an appealing candidate to increase transduction rates by both viral and nonviral (e.g. utilizing cationic liposomes) mediated delivery mechanisms.
Mice, humans, and certain fish have two or more different protamines, whereas the sperm of bull, boar, rat, rabbit, guinea pig, and ram have one form of protamine.
The 2 human protamines are denoted PRM1 and PRM2.
Examples of protamines from fish are:
Protamine structure 
The secondary and tertiary structure of protamine is not known with certainty, but several proposals have been published.
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- ^ Kenneth Cornetta, W.French Anderson (1989). "Protamine sulfate as an effective alternative to polybrene in retroviral-mediated gene-transfer: implications for human gene therapy". Journal of Virological Methods 23 (2): 187–194.
- ^ Sorgi, F L., et. al (1997). "Protamine sulfate enhances lipid-mediated gene transfer". Gene Therapy 4 (9): 961–968.
- ^ Martins RP, Ostermeier GC, Krawetz SA (December 2004). "Nuclear matrix interactions at the human protamine domain: a working model of potentiation". J. Biol. Chem. 279 (50): 51862–8. doi:10.1074/jbc.M409415200. PMID 15452126.
- ^ Vilfan ID, Conwell CC, Hud NV (May 2004). "Formation of native-like mammalian sperm cell chromatin with folded bull protamine". J. Biol. Chem. 279 (19): 20088–95. doi:10.1074/jbc.M312777200. PMID 14990583.
- ^ Biegeleisen K (August 2006). "The probable structure of the protamine-DNA complex". J. Theor. Biol. 241 (3): 533–40. doi:10.1016/j.jtbi.2005.12.015. PMID 16442565.
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