Globular shape of high molar mass inulin revealed by static light scattering and viscometry

The behavior of two high molar mass inulin-type fructans in dilute aqueous and dimethyl sulfoxide solution was investigated. We performed static light scattering experiments (SLS) and viscometry with the polymer synthesized i n vitro using the fructosyltransferase (FTF) of Streptococcus mutans that w as expressed as a fusion protein in transgenic Escherichia coli. In additio n, high molar mass inulin of Aspergillus sydowi (A. sydowi) was synthesized by incubating conidia with highly concentrated sucrose solution. This poly mer was characterized by SLS and high-performance size-exclusion chromatogr aphy. All samples showed small root-mean-square radii of gyration with respect to their very high molar mass. Since this suggests a compact conformation of the molecules in both solvents, the dependence of reduced osmotic modulus M -w/M-app on parameter X = A(2)/M(w)c was studied by SLS. For all measuremen ts, we found an agreement between experimental Values and theoretical curve s for hard spheres. Hydrodynamic data also point to a globular shape of hig h molar mass inulin in dilute solution. The determination of branches for inulin synthesized by FTF and by A. sydow i conidia indicates that both polymers are beta-(2 --> 1) linked polyfructa ns with 5-7% beta-(2 --> 6) branches, which is in agreement with the obtain ed globular molecular shape in dilute solution. (C) 2000 Elsevier Science L td. All rights reserved.