Protamine sulfate is a polycationic peptide compound with anti-heparin activity. It can neutralize the anticoagulant effects of heparin, enhance lipid-mediated gene transfer, and is commonly used to establish cystitis models.

Protamine sulfate, a 5-kDa cationic polypeptide derived from salmon sperm, demonstrates a concentration-dependent, partial, and reversible inhibitory effect on thrombin's ability to convert fibrinogen to fibrin. This compound also binds negatively charged unfractionated heparin (UFH), concurrently downregulating thrombin generation through the inhibition of factor V activation.