Figure 3.

Force-extension curves for native (A) and periodate-oxidized pectins (B). In A, we demonstrate that the conformational transitions underlying the enthalpic components of pectin elasticity are reversible. The blue trace represents the recording obtained on stretching and the red trace, on relaxing a single pectin. The recording did not show any hysteresis and was separated only to reveal the forward and backward traces. Pulling speed, 0.5 nm/ms. (B) The force-extension curve of periodate-oxidized galactouronan (Inset) does not reveal any significant enthalpic elasticity and represents the extensibility of a FJC of very short (l_K = 0.19 nm) and rigid (S_E = 70,000 pN⋅nm⁻¹) segments.