Protamine

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.

Function
When mixed with insulin, protamines slow down the onset and increase the duration of insulin action (see NPH insulin).

Protamine sulfate is an antidote for heparin. The dose of protamine sulfate used to reverse heparin is 10 mg IV for every 1,000 Units of unfractionated heparin. Care should be exercised in the patient who has ingested NPH insulin (Neutral Protamine Hagedorn) as these patients can sustain an allergic reaction to protamine sulfate. Protamine sulfate also partially reverses enoxaparin (reverses Factor Xa inhibition by 60%).

Examples
Mice, humans, and certain fish have 2 or more different protamines, whereas the sperm of bull, boar, rat, rabbit, guinea pig, and ram have one form of protamine.

Human
The 2 human protamines are denoted and.