Molecular origins of acetan solution properties.

Acetan is a branched acidic heteropolysaccharide secreted by Acetobacter xylinum. X-ray diffraction studies of oriented fibres suggest non-crystalline helices with fivefold symmetry and a pitch of 4.8 nm. Optical rotation and circular dichroism studies are consistent with the retention of the helical structure in solution and a helix-coil transition upon heating and cooling. Aqueous solutions yield high 'low shear rate' viscosity and shear-thin upon shearing.