FIGURE 1.

Elasticity of single native heparin molecules isolated from mast cell secretory granules. (A) Simplified diagram of heparin structure. Heparin consists of repeats of two dimers: a 1→4 linked α-L-iduronic acid (IdoA) and α-D-glucosamine (GlcN) (∼80%) and a 1→4 linked β-D-glucuronic acid (GlcA) and α-D-GlcN (∼20%) with the average number of dimers in a heparin chain ranging from 50 to 150. (B) Force-extension curves of single native heparin molecules obtained from the heparin matrix of mast cell secretory granules. Heparin was dissociated from the protein backbone at alkaline pH (Fernandez et al., 1991). (C) Normalized force-extension curves of native heparin superimpose on each other, proving that the recordings were made on single molecules. The relative increase in the contour length of heparin molecules due to its enthalpic elasticity (a hump in the curves) was determined to be 11.6 ± 3.1% (n = 12). In all cases, the extension x, was normalized by the length of the molecule measured at 100 pN.