Double helix of Agrobacterium tumefaciens succinoglycan in dilute solution

Succinoglycan samples ranging in weight-average molecular weight from 1.4×105 to 10.5×105 (in 0.1 M aqueous NaCl at 25°C), prepared from native succinoglycan by sonication, were investigated by static light scattering and viscometory in 0.1 M aqueous NaCl. It is well known that the conformation of the polysaccharide changes at around 65°C. In order to confirm the conformation of the polysaccharide, the property of the polysaccharide in dilute solution was studied at both 25 and 75°C. The molecular weight of a sample at 25°C is the double of the value at 75°C. The molecular weight dependence of 〈s2〉Z and [η] for succinoglycan shows that the polysaccharide is a rod-like polymer at 25°C and behaves like a semi-flexible polymer at 75°C in 0.1 M aqueous NaCl. Moreover, the linear mass density of the polysaccharide was almost twice that expected for single succinoglycan molecules. These results indicate that the conformation of the polysaccharide would be a double helix at 25°C and the helix melts to a single strand behaving as a semi-flexible chain above 65°C.