Force spectroscopy on single xanthan molecules

The mechanical properties of native and denatured xanthan are measured on t he molecular scale using an AFM. The single molecule force spectra of nativ e and denatured xanthan show big differences. For ordered native xanthan, a long plateau at around 400 pN is found, this transition is an irreversible process. However, the plateau disappears for denatured xanthan, only monot onic rising of the force versus extension is observed. The big difference i s consistent with the different conformation of native and denatured xantha n. Native xanthan is assumed to exist as an ordered double-stranded helix, however, denatured xanthan is a disordered single strand. The irreversible transition process for native xanthan is attributed to the splitting of the double-strand helix.