The C-terminus of type I collagen is a major binding site for heparin.

The binding of collagens and fragments of type I collagen to heparin was studied by gel electrophoresis and affinity chromatography. Samples bound in 150 mM NaCl/10 mM Hepes (pH 6.5) were eluted with 2 M NaCl, 6 M urea, or a linear gradient of 0.15-1.0 M NaCl. The triple-helical conformation was shown to be essential for binding. The vertebrate collagenase-generated C-terminal fragment, TCB, was shown to have greater binding affinity for heparin than the N-terminal TCA fragment. Both type II collagen and the NC1 domain of type IV collagen bound to heparin, whereas pepsin-solubilized tetrameric type IV failed to bind.